X-37B Spaceplane mission OTV 8 located on orbit

OTV 8 imaged by Kevin Fetter 5 hours after launch. Image (c) Kevin Fetter, used with permission

OTV 8, the 8th mission of the US Space Force's X-37B Spaceplane, launched on 22 August 2025 at 03:50 UTC. It has been catalogued as 2025-183A (cat. nr. 65271) under the name of  'USA 555', along with a second payload, called LIMASAT (2025-183B, 65272). The latter has probably been dispensed from the OTV 8 service module.

Five hours after launch, Kevin Fetter managed to observe OTV 8. Above is one of his images, showing OTV 8 as a short bright trail in a partly cloudy sky. 

A preliminary orbit fit suggests that OTV 8 is in a 327 x 334 km, 49.5 degree inclined orbit [update 25 Aug 2025: the latest improved orbit update shows it in a 331 x 342 km, 49.5 degree inclined orbit]: a slightly (~20 km) lower orbital altitude than my initial pre-launch guess but otherwise a quite comparable orbit.

Click image to enlarge

 

An overview of the OTV missions so far: 

MISSION  ORBITER  LAUNCH   INCL   ORBIT   DURATION
--------------------------------------------------
OTV 1    I        2010     40.0   LEO     224 days
OTV 2    II       2011     42.8   LEO     468 days
OTV 3    I        2012     43.5   LEO     674 days
OTV 4    II       2015     38.0   LEO     717 days
OTV 5    II       2017     54.5   LEO     780 days
OTV 6    I        2020     45.0   LEO     909 days
OTV 7    II       2023     59.1   HEO     435 days
OTV 8    I        2025     49.5   LEO         tbd
--------------------------------------------------

Bad weather in the Netherlands has so far precluded me from trying to observe the latest launch.
 

EDIT (24 August 2025): 

I imaged both the USSF-36 payloads (OTV 8 and Limasat) in the early morning of 24 August, see this follow-up blogpost with footage. 

Recovery of the X-37B spaceplane OTV 7

click to enlarge

 

The classified US Space Force X-37B spaceplane OTV 7 (2023-210A) was launched on 29 December 2023, in an unusual Highly Elliptical Orbit. Five weeks after launch, in the first week of February 2024, it was found on-orbit by Tomi Simola from Finland in a 38600 x 300 km, 59.15 degree inclined orbit (see this earlier blogpost). We followed it for a month and then lost it: the last observation was on March 15.

But now it has been recovered! On the night of July 30-31, I was imaging geosynchronous objects when I noted a short trail made by an unidentified interlooper.  Mike McCants identified the UNID as OTV 7.

The image in top of this post (one out of four images spanning half an hour) shows the short faint trail created by OTV 7. The ~9 by 4.5 meters large X-37B spaceplane was near apogee of its orbit at that time, at about 35535 km altitude (and a range of some 38775 km to my observing location). The image is a 10-second exposure with a ZWO ASI 6200 MM PRO and Samyang 1.2/85 mm lens, and shows only a small part of the original image. It was taken from Leiden, the Netherlands.

Weather next initially conspired against me, but last night, August 3-4, I again observed it, some 25 minutes late on the initial elset estimate. This is a small part of one of the images, shsowing the faint trail created by OTV 7:

click image to enlarge

The observing conditions were very dynamic this time: after rainshowers, small but bright, stamp-sized clearings were sometimes present in the clpud cover. I managed to image the object through such gaps in the cloud cover a few times over an half-an-hour-period, 25 minutes late on the preliminary orbit. 

Below is an example of what I am talking about when I say "stamp-sized clearings": this is the last image (reduced in size as the true image is 9576 x 6388 pixels) on which I could find it. All the white is clouds....:

click to enlarge

The new observations constrain the orbit a little bit better: 314 x 35552 km, 59.15 degree inclined. A provisional elset:

OTV 7
1 58666U 23210A   24216.90625742 0.00000000  00000-0  00000+0 0    01
2 58666  59.1511 329.1636 7247171 178.5736 186.3429  2.29027449    03

rms 0.004 deg   from 9 obs, arc July 30.96 - Aug 3.96 UTC

Below is a comparison between the (forward propagated) orbit from March (red), and the current orbit (white). Apogee is some 2300 km lower than it was in March (and this is not due to natural orbital decay, but due to manoeuvering). The orbital plane itself is still similar.

click image to enlarge

[UPDATED] OTV 6 (USSF 7), the next X-37B launch, appears to go into a 44-degree inclined orbit

OTV 6.  Image: US Air Force. Click to enlarge

If weather cooperates, the next X-37B launch, mission OTV 6 ,also known as launch USSF 7, is slated for May 16, with backup dates on May 17 and 18 in case launch is postponed. The small uncrewed space plane will be launched for the US Air Force by the United Launch Alliance, with an Atlas 5 rocket, from Cape Canaveral SLC-41.

Navigational Warnings have now appeared for this launch, which shed light on the launch window and the orbit aimed for:

NAVAREA IV 388/20(GEN).
WESTERN NORTH ATLANTIC.
FLORIDA.
1. HAZARDOUS OPERATIONS, ROCKET LAUNCHING
   161224Z TO 161453Z MAY, ALTERNATE
   171314Z TO 171532Z AND 181354Z TO 181434Z MAY
   IN AREAS BOUND BY:
   A. 28-36-51N 080-35-57W, 28-41-00N 080-26-00W,
      28-36-00N 080-23-00W, 28-31-36N 080-33-34W.
   B. 32-28-00N 075-12-00W, 33-50-00N 072-51-00W,
      33-08-00N 072-17-00W, 31-45-00N 074-41-00W.
   C. 38-43-00N 062-38-00W, 40-23-00N 058-26-00W,
      39-18-00N 057-47-00W, 37-34-00N 061-56-00W.
2. CANCEL THIS MSG 181534Z MAY 20.//


HYDROPAC 1415/20(74,75).
SOUTHEASTERN INDIAN OCEAN.
DNC 03, DNC 04.
1. HAZARDOUS OPERATIONS, SPACE DEBRIS
   161319Z TO 161528Z MAY, ALTERNATE
   171409Z TO 171607Z AND 181449Z TO 181509Z MAY
   IN AREA BOUND BY
   36-03S 096-54E, 33-40S 098-30E,
   37-32S 108-22E, 40-03S 107-00E.
2. CANCEL THIS MSG 181609Z MAY 20.//


The launch azimuth defined by the three launch hazard areas A, B and C in the Atlantic Ocean and the location of the Centaur upper stage deorbit zone in the Indian Ocean, point to a launch into a ~44-degree inclined orbit, give or take half a degree. The Centaur upper stage will be deorbitted about half a revolution (55 minutes) after launch.

The following map depicts the hazard areas and the trajectory of the first orbit, for a 44-degree inclined orbit and an orbital altitude of ~350 km. The latter orbit fits the locations of the hazard zones well, and the ~55 minutes time difference between the start of the launch windows and the start of the Centaur upper stage deorbit windows in the Navigational Warnings combined with the position of the deorbit zone, fits a ~350 km altitude orbit:

Click map to enlarge

Launch into a 44-degree inclined orbit unfortunately means I do not get to track it from the Netherlands, as my observing location is too high north in latitude to see it in such an orbit. Following the previous OTV 5 launch, that went into a 54.5 degree inclined orbit and could be well observed from the Netherlands, I had some hopes for OTV 6, but alas no, it is not to be apparently...

A 44-degree orbital inclination would be similar to mission OTV 3 from 2012-2014. These are the orbital inclinations of all past OTV missions:

Mission     inclination    operational period        flight duration
OTV 1       40.0^o          22/04/2010 - 30/11/2010   224 days
OTV 2       42.8^o          05/03/2011 - 16/06/2012   468 days
OTV 3       43.5^o          25/10/2012 - 17/10/2014   675 days
OTV 4       38.0^o          20/05/2015 - 07/05/2017   718 days
OTV 5       54.5^o          07/09/2017 - 27/10/2019   780 days
OTV 6       44.0^o ?        16/05/2020 - ?

With regard to the upcoming launch, the given launch windows for May 16 and the two backup dates are curious. These launch windows are not the same duration (May 16 is 2h 29m in duration; May 17 is 2h 18m in duration; and May 18 only 40 minutes in duration).  They shift oddly from date to date too. The start of the given windows shifts 50 minutes between May 16 and 17; and shifts 40 minutes between May 17 and 18. It moreover shift to a later time between consecutive dates: while a given targetted orbital plane would make the launch shift to an earlier time, not a later time

Perhaps this is done to obfuscate the launch time and RAAN aimed for (or maybe it is just simply Range availability at play). If we look at the common ground: all three launch windows have a potential 10-degree wide RAAN window between 331^o.14 and 341^o.17 in common, so perhaps that is what is aimed for. If that interpretation is correct, this would lead to the following potential 40-minute launch windows, shifting back by 4 minutes each day:

16 May     13:58 - 14:38 UT
17 May     13:54 - 14:34 UT
18 May     13:50 - 14:30 UT

But of course, it is always possible that they launch straight away at the 12:24 UT opening of the May 16 window...we will see!

[Edit 15 May 2020 23:20 UT: but see note at end of post!]

A lot has been written about the X-37B and its purpose, and there are a lot of persistent misconceptions regarding the fact that it is a "space plane" (see my blogpost "X-37B fact and fiction" from July 2019).

Far from being a nefarious device, the X-37B appears to be a testbed for experimental space technology. According to the US Space Force, one of the things that will be tested during the next OTV 6 mission is an experiment to transmit solar power by microwave. It will also contain two NASA experiments that study the effects of radiation on materials and seeds, and it will deploy at least one military cubesat, FalconSat 8 (the previous OTV mission, OTV 5, released three cubesats).

The US Space Force Press Release also indicates that, as a first, OTV 6 will be fitted with a "service module" to the aft of the vehicle, that will house experiments (previous OTV missions housed experiments in the cargo bay). It will be interesting to see what happens to this service module at the end of the mission.

Addendum 13 May 22:05 UT:
More on the microwave experiment in this article (HT to Brian Weeden). It seems it is not so much transmission by microwave, but the generation of microwaves from solar power, which is then send through a cable, if I get it correctly. Anyway: something with microwaves...

Addendum 15 May 23:20 UT:

Bob Christy wrote a very interesting analysis on his Zarya blog, in which he links similar odd jumps in past OTV launch windows to times of close KH-11 passes, the idea being that these KH-11 satellites image the OTV after launch to see whether everything is allright. If that is correct, then this leads to four possible launch times on May 16: 12:24, 13:15, 14:06 and 14:53 UT.
My estimated elsets for these four launch times can be found here.

Addendum 18 May 13:55 UT:

OTV 6 launched on 17 May 2020 at 14:13 UT. A pre-launch estimated elset can be found here;  a preliminary radio-observation based orbit here.

Based on the preliminary radio elset, OTV 6 appears to have been inserted into a 45-degree inclined orbit at ~390 km altitude. The ground track repeats every 3 days:

click to enlarge

Here is how the launch track based on the radio orbit (red dashed line) compares to my pre-launch estimated launch track based on the locations of the hazard areas from the Navigational Warnings (blue dashed line):

click map to enlarge

Launching cubesats from the X-37B OTV 5: lifetime modelling with GMAT

image: USAF

Last week, CSpOC issued catalogue entries for three cubesats released as part of the X-37B mission OTV 5.

It concerns USA 295 (2017-052C), USA 296 (2017-052D) and USA 297 (2017-052E). No orbital data are given, but the catalogue entry did explicitly indicate that all three are no longer on orbit.

That cubesats were released as part of this X-37B mission had been clear from a US Air Force statement made after completion of the OTV 5 mission in October last year. The wording of that statement is however ambiguous: while most analysts take it to mean the cubesats were released by OTV 5, it is also possible that they were released as ride shares by the upper stage of the Falcon 9 rocket that launched OTV 5 in 2017.

In this blog post, I will do an academic exercise aimed at guessing when, at the latest, these cubesats could have been released by OTV 5, assuming release from the latter.

OTV 5, the 5th X-37B mission, was launched from Cape Canaveral on 7 September 2017. It landed at the Kennedy Space Center Shuttle Landing Facility on 27 October 2019, after 780 days in space. Unlike previous missions that were all launched in 38-43 degree inclined orbits, this one was launched into a 54.5 degree inclined orbit. Combined with the fall launch date, this meant it took our tracking network a while to locate it on-orbit: the first positive observations were made in April 2018, half a year after launch.

From April 2018, when we started to track it, to October 2019, when it landed, OTV 5 orbitted at various orbital altitudes between 300 and 390 km altitude (see diagram below):

click diagram to enlarge

The CSpOC catalogue entry lists all three cubesats that were released as part of this mission as "no longer on orbit". Assuming they ended their orbital life by natural decay (rather than, for example, being retrieved by OTV 5 again at a later stage, which is in theory certainly possible!), the fact that they were no longer on orbit by 11 February 2020 might yield some constraints on when they could have been released.

To get some idea of the orbital lifetime of a cubesat released from OTV 5, and spurred on to do so by Jonathan McDowell, I ran several GMAT models in which I modelled a 5 kg 3U cubesat released at three altitudes: 400 km, 360 km and 325 km.

We do not know the actual orbital altitude of OTV 5 at that  moment. Nor do we know when the cubesats were released. Hence the three altitude variants. The start point of the modelling was an assumed release into the OTV 5 orbit on October 7, 2017, one month after launch of OTV 5.

For each cubesat, the models were run in two variants: one with the cubesat in minimal drag orientation (0.01 m² cross section), and one with the cubesat in maximal drag orientation (0.03 m² cross section). I used the MSISE90 atmosphere in the model, with historic Space Weather data for October 2017 to February 2020 and estimated solar and geomagnetic activity parameters from the 'early cycle' variant of the GMAT Schattenfile for dates past early 2020.

For the three assumed orbital altitudes and an assumed release one month after OTV 5 launch, the GMAT data produce the orbital decay plots below. In these plots, the red data are for minimal drag orientation, the blue data for maximal drag orientation. If the cubesats in question were similar to NRO's Colony II cubesats, then the red minimum drag orientation curves probably represent the orbital evolution best. If they were more like Colony I cubesats, then the blue maximal drag curves are more representative.

Taking the minimal drag variants, and under the assumption that the cubesats were 3U cubesats and not retrieved on-orbit by OTV 5 at a later stage, the suggestion is a release below 350 km. Released at higher altitudes, they would still be on-orbit.

Assuming reentry before 11 February 2020 after natural orbital decay, a minimal drag orientation and release no lower and no higher than 325 km, the latest possible moment of release would be late August 2018, give or take a month to account for the uncertainties.

It appears we can rule this out however, because we know that OTV 5 was orbiting at 380 km altitude, not 325 km altitude, at that time. So the best guess (although one under many assumptions) is a release some time before August 2018, i.e. within 1 year after the launch of OTV 5.

It is still possible that the cubesats were released at a later date, but next retrieved while still on-orbit by OTV 5. If the cubesats were smaller than a 3U cubesat, a later release than August 2018 is possible as well.

Finally, given the ambiguity in US Air Force Statements on the matter, it is also possible that the cubesats were released from the Falcon 9 upper stage on the day of launch.

For more about the X-37B, and especially the active myth-making that seems to be at play around this secretive space-plane, see my earlier post here.

OTV 5 rising in April 2018. Click image to enlarge

X-37B fact and fiction

X-37B. Photo: USAF

If there is one classified space object that speaks to the public's imagination, then it is the US Air Force's  X-37B robottic space plane, also known as Orbital Test Vehicle (OTV).  These 9 meter long uncrewed spacecraft have wings, with a wingspan of 4.5 meter, and look like a mini Space Shuttle. They are launched on a rocket like a normal satellite, but return to earth by landing like an airplane (or indeed like the Space Shuttles did). They have a payload bay of 2.1 by 1.2 meter in which they carry experiments and from which they could perhaps also release and retrieve small satellites. They are launched in very low orbits, between 250 and 450 km orbital altitude (i.e. generally below the orbit of the ISS).

The US Air Force has two X-37B's and is currently flying it's 5th OTV mission with one of them, with 685 days on orbit on the day of writing.

The winged design and the coloquial 'space plane' lead many people to think the X-37B flies and banks like an airplane or a Star Wars X-wing fighter while in space - its infamous purported "manoeuverability", a notion recently fuelled again by remarks of former SecAF Heather Wilson (see below).

This is mostly a misunderstanding and part of the mythos that surrounds the X-37B: in space, the wings of the X-37B are useless and it behaves and orbits the earth like any other satellite. The X-37B does not change its orbital plane at a whim - or at least not generally. That is quite clear from amateur monitoring of the five OTV missions so far.

In this post I will show that the only significant manoeuvers the OTV's make are frequent alterations of their orbital altitude: they do not significantly change orbital plane during a mission. Periodically changing orbital altitude is something other satellites do too, so the X-37B is not special in this either, except that during recent OTV missions the X-37B's have done this more often than ordinary satellites typically do. And let me add, so you understand me well: you don't need (or indeed use) wings for that. These orbital altitude changes are done with an engine burn, just like 'normal' satellites do.

The X-37B OTV 5 filmed by the author on 26 June 2019

The wings of the X-37B are not for manoeuvering in space, but primarily for use in the lower atmosphere upon its return to earth, when it lands like an aircraft (as the Space Shuttle did). Yet every now and then, the myth of the supposed wing-supported "manoeuverability" pops up again, and connected to it is a whole ecosystem of suspicions and theories about the potential "function" of the X-37B - most notoriously the (almost certainly incorrect) notion that it is some kind of "Space Bomber" ready to be flown to any target on earth within 90 minutes to drop a destructive weapon. The Space Treaty, to which the USA is a signatory, prohibits to deploy weapons from space, and it is really unlikely that the X-37B is such a 'space bomber'.

The X37-B instead likely is a testbed for new space hardware, testing new technologies under real space conditions and then returning them to earth for inspection. We know for example that during the OTV 4 mission, a XR-5a Hall-effect thruster was tested. The frequent changes in orbital altitude are part of this: testing space hardware under various drag regimes.

So what about that "manoeuverability" then? New fuel was fanned on the idea of extraordinarily "manoeuverability" recently by intriguing statements made by former SecAF Heather Wilson. She claimed that the X-37B:

"Can do an orbit that looks like an egg and, when it's close to the Earth, it's close enough to the atmosphere to turn where it is. [...] Which means our adversaries don't know -- and that happens on the far side of the Earth from our adversaries -- where it's going to come up next. And we know that that drives them nuts."

Two things are apparently being claimed here:

(1)  The X-37B can manoeuvre by briefly dipping into the upper atmosphere;

(2)  This makes the X-37B difficult to track.

The wording of the statement is wonderfully opaque, but Wilson seems to suggest that the X-37B can seriously change its orbital inclination by briefly dipping into the upper atmosphere and using its wings to manoeuvre.

I have two problems with this. One is that bringing the X-37B down into the upper atmosphere by an engine burn (there is no other way), have it change orbital plane by using the wings, and then do a burn to get back to orbital altitude again, probably costs as much fuel as a more regular on-orbit engine burn to change orbital plane. So where is the gain in using this dip-and-wing-manoeuvre?

The other problem I have, is that I do not see the claimed behaviour in our tracking data. Contrary to the impression that Wilson is trying to give us, i.e. that the X-37B's are difficult to track due to the tricks they perform, the X-37B OTV missions have been regularly tracked by our amateur network. And we do not see significant changes in the orbital plane during a given OTV mission.

The X-37B OTV 5 imaged by the author in April 2018 (click to enlarge)

Looking at the tracking data we have for these X-37B missions, they show only very minor changes in orbital inclination during a given mission. There is no evidence for sudden, significant changes in the orbital plane, as is illustrated by these diagrams that for each OTV mission plots the orbital inclination against time (the data are from observations by the satobs amateur network):

The only exception appears to be mission OTV 4, which does show a temporary change in orbital inclination and then back again in the last quarter of 2016. The orbital plane change is of little significance however (only 0.6 degrees) and could have been done by a normal engine burn. So if the X-37B indeed can use a drop into the upper atmosphere to make use of it wings to significantly change orbital plane, they so far do not seem to have clearly demonstrated this capability.

(the changes in orbital inclination at the end of the OTV 2 and OTV 3 missions, probably are in preparation for landing).

What the X-37B missions in contrast do have demonstrated, especially during the last two missions, are repeated changes in orbital altitude and orbital eccentricity (in Wilsons words: it "can do an orbit like an egg"). This is illustrated by these plots of the apogee and perigee altitudes against time for the five OTV missions so far:

As I already mentioned this is something other satellites do too, so the X-37B is not particularly special in this either, except that during recent OTV missions the X-37B's do this more often than ordinary satellites typically do. The changes in orbital altitude probably are related to testing equipment under different drag, gravity and irradiation regimes.

So the X-37B missions so far set themselves apart from regular satellite missions by their low orbital altitudes and frequent changes in orbital altitude (in which the wings play no role at all). They can do so because their missions are relatively short compared to a typical satellite mission. Unlike a regular satellite, at one point they will land and be refuelled, and then relaunched after a while.

But as intriguing as the suggestions are, the orbital history of the five X-37B OTV missions so far do not evidence the alledged manoeuverability in orbital plane.

Nor of course, are the X-37B that difficult to track as is claimed. Our amateur network regularly observed and observes the OTV missions. We might lose the OTV for a (usually brief) moment when it has made a manoeuvre to a higher or lower orbit, but a plane scan is enough to relocate it (and as the diagrams above show, they do not manoeuvre daily or even weekly).

So Wilson's remarks appear to be just part of the myth-making around the X-37B.

Pinpointing the OTV 5 orbital manoeuvre on 19 April 2018

click map to enlarge

As related in a previous post, the X-37B robottic space plane OTV 5 made an orbital manoeuvre on the 19th, lowering its orbital altitude from ~355 km to ~315 km.

It has been observed in its new orbit enough by now (pass predictions for yesterday evening were spot on), to allow an analysis to reconstruct the time and location of the manoeuvre. This can be done by looking for a moment where the positions in the old orbit and the new orbit were close.

Using Mike's pre-manoeuvre OTV 5 orbit of epoch 18104.41928168 and my own post-manoeuvre orbit solution of epoch 18112.84880111, and feeding these into the COLA program written a long time ago by Rob Matson, the resulting time of coincidence is 19 April 2018 at 5:20 UT.

OTV 5 was near perigee and in its descending node at the time, over west Africa, as can be seen on the map above. Manoeuvres typically happen near the nodes and near either perigee or apogee, so that fits well with this reconstructed moment of manoeuvre.

Since the manoeuvre entailed both a lowering of the perigee and a lowering of the apogee, the time and location listed above is likely the second of two manoeuvre moments.

The first manoeuvre burn probably happened near 4:35 UT, near apogee and the ascending node of the original orbit, south of Hawaii. This burn lowered the perigee altitude of the orbit to 310 km. Next, a second burn lowering the apogee altitude to 323 km was conducted half an orbital revolution later at 5:20 UT, near perigee and the ascending node of the orbit over west Africa. The two points are depicted by red circles in the map above.

Past OTV missions frequently made such manoeuvres between different orbital altitudes. They probably are meant to be able to test experimental technology in the payload bay under various thermospheric density and irradiation regimes.

Meanwhile, we continue to track OTV 5 in its new orbit. My observations yesterday were hampered a bit by an untimely field of clouds, but I did get some astrometry. Here is some imagery from yesterday, showing OTV 5 ascending amidst a thin cloud cover (bright star in clouds at right is Capella):

click photograph to enlarge

OTV 5 or Zuma? A brief explanation why this object is OTV 5 and not Zuma

click image to enlarge

The image above shows the US Air Force's "secret" X-37B space plane OTV 5 ascending in the western sky (the two bright stars above the roof are Castor and Pollux), in the evening of 21 April 2018.

I was asked the question: "how do we know this is OTV 5? Why can't it be Zuma?". I will explain here why it is definitely OTV 5 and definitely not Zuma.

The key is in the orientation of the orbital plane. Both OTV 5 and Zuma were launched from Cape Canaveral into a northwest direction, towards azimuth 40-50 degrees (see map with launch hazard zones below). That direction establishes the orbital plane the objects were launched into.

click to enlarge

From our tracking of the OTV 5 candidate the past 10 days, we have the orbital plane this object is moving in. We can project that orbital plane back to the launch dates of both OTV 5 and Zuma.

For the launch date and launch time, it should pass over the launch site, with a correct orientation in terms of direction. That means, in this case: it should pass over Cape Canaveral, into a northeastern direction.

Now let us first do that for OTV 5, which was launched by SpaceX from Cape Canaveral pad 39A on 7 Sept 2017 at 14:00 UT. The 3D plot below shows the orbital plane of the object we track projected backwards, for the moment of OTV 5 orbit insertion (7 Sep 2017, ~14:09 UT):

click to enlarge

As can be clearly seen, the orbital plane we established for the object we have been tracking the past few days, for this date and time lines up with the launch site, and it is oriented into the correct direction (southwest to northeast). This strongly indicates that the object we track is from the OTV 5 launch.

If we do the same for the Zuma launch, we do not get a good match. Zuma was launched by SpaceX on 8 Jan 2018 at 01:00 UT from Cape Canaveral pad 40. The 3D plot below shows the orbital plane of the object we track projected backwards, for the moment of Zuma's orbit insertion (8 Jan 2018, ~01:09 UT):

click to enlarge

As we can see, the orbital plane we established for the object we have been tracking the past few days, for this date and time does not line up with the launch site, and it is moreover oriented into the wrong direction too (northwest to southeast instead of southwest to northeast: a 90-degree angle!). This strongly indicates that the object we track is not from the Zuma launch.

(As avid readers of this blog know, Zuma presumably failed to detach from the Falcon 9 upper stage due to a faulty adapter provided by the satellite's builder Northrop Grumman, and reentered with the upper stage a few hours after its launch).

So the object's orbital plane lines up with a launch from Cape Canaveral on 7 Sept 2017 and orbit insertion at 14:09 UT, the launch date of OTV 5. Ad to this the very low orbit which was also typical for past OTV missions, and it is very clear that the object we are currently tracking is the X-37B mission OTV 5.

Below is a video of OTV 5 which I shot yesterday evening, 21 April 2018:

Imaging the X-37B Space Plane OTV 5 post-manoeuvre

click image to enlarge

The image above shows the secretive X-37B Space Plane OTV 5, a robottic mini space shuttle flown by the US Air Force, over my house in Leiden, cruising through Leo (the bright star above the chimney is Regulus). It was a bright, easy naked eye object with a brightness of magnitude +1.

In a previous post I detailed how (and why), following the launch in September 2017, we had a hard time tracking down the whereabouts of this fifth OTV mission. Untill Cees Bassa located it on April 11th, in a 54.4 degree inclined orbit. It is the first OTV mission bringing it to the latitudes of the Netherlands.

Clouded weather in the Dutch coastal region after Cees' recovery prevented me from seeing it untill yesterday. During the past week, OTV 5 moved from morning passes to evening passes. Weather improved too medio last week, but still OTV 5 initially escaped me. Because it manoeuvered!

On April 18th, a week after it was first located in orbit, OTV 5 made a manoeuvre. It was a no-show for several observers, including me, on the 19th, but two observers, Tristan Cools in Belgium and Marian Sabo in Slovakia, reported an "unidentified" object some 8 minutes earlier (which means it passed while I was setting up my camera on the 19th). Based on Tristan's photograph of that object, a post-manoeuvre orbit was guessed by Mike McCants as well as by me. Yesterday evening on the 20th, we were ready to look for it, and we did recover OTV 5, a few minutes in front of the estimated new orbit.

The new orbit is still preliminary, but it seems as if the orbit has been lowered from a ~355 km circular orbit to a 307 x  320 km orbit. In a few days, when we have more observations, we'll know more about the new orbit, and when the manoeuvre exactly happened.

The video below which I shot yesterday evening shows OTV 5 cruising through the Coma Berenice cluster:



This was my very first observation of an X-37B! Very cool to see this enigmatic object pass in my own sky. Given that previous OTV missions frequently manoeuvered, it will be an interesting object to follow.

All kinds of nefarious motives and purported specific targets have been ascribed to the X-37B program by the aluminium hat brigade, but the reality probably is that the X-37B is an experimental test-bed for new space technologies, testing these under real space conditions and at various thermospheric regimes, over a prolonged time period, before retrieving them.

I do find it interesting though that this new OTV mission is in a 54.4 degree inclined orbit, rather than the previous 38-43 degree inclined orbits (see comparison in my previous post). Over the past year we have now seen three experimental missions going (or planned to go) into 50-55 degree inclined orbits: USA 276; the failed Zuma; and OTV 5. All three are clearly experimental missions. For Zuma, I suspect it was meant as an experimental radar satellite, and maybe OTV 5 tests radar as well. Or maybe not.

At any rate, I welcome this new attention to ~50-55 degrees inclination, as objects in such orbits are well observable from my 52-degree latitude in the Netherlands.

X-37B OTV-5 mission located on orbit

OTV-5, The fifth mission of the US Air Force' X-37B  robottic mini-shuttle, was launched from Cape Canaveral on 7 September 2017 on a SpaceX Falcon 9 rocket. Until last week, OTV-5 had not been located by amateur satellite trackers, and that was somewhat curious, as we did locate and track the previous four missions.

But now OTV-5 has been finally found. In the early morning of April 11, 2018, Dutch satellite tracker Cees Bassa imaged a bright unidentified satellite in a ~54 degree inclined orbit. It was seen again by Cees two days later, on April 13. Ted Molczan managed to link it to a lone sighthing of an unidentified object done by Russell Eberst in Scotland back in early October 2017 that was already suspected to perhaps be OTV-5 at that time (several of us, including me,  had tried to recover the object Russell observed in the next few nights that October, but failed).

OTV-5 immediately was suspected as the identity for this object. It was in a very low, ~355 km circular orbit, which is lower than usual for satellites, but which fits with the characteristics of previous OTV missions.

The orbital plane the object is moving in passed over Cape Canaveral at the moment OTV-5 was launched (see below, which shows the location of the orbital plane for the moment of OTV-5 orbit insertion on 7 September 2017). So that fits nicely, and as a result we are quite confident that this is OTV-5.

click to enlarge

There is a difference with previous OTV missions: OTV-5 is in a 54.5 degree inclined orbit, which is a substantially higher orbital inclination than that of previous OTV missions which were flown at orbital inclinations between 38.0 degrees and 43.5 degrees, as can be seen in this diagram below where the current OTV-5 mission orbit is white, and previous OTV mission orbits are red:

click to enlarge

But this actually fits with information released on the OTV-5 mission by the US Air Force, which prior to the launch of OTV-5 stated that:

"The fifth OTV mission will also be launched into, and landed from, a higher inclination orbit than prior missions to further expand the X-37B’s orbital envelop." 

I am very happy that OTV-5 was launched, as it now turns out, into a 54 degree inclined orbit, as for the first time this will give me a chance to see an X-37B OTV mission from the Netherlands. OTV-5 will actually pass over my country (and even somewhat north of it), while previous OTV missions passed over southern Europe only. The previous four missions therefore were not visible from my country, due to their lower orbital inclination.

An obvious question is: why did it take so long to find OTV-5? I have some answers to this that might explain.

First, I think many amateurs subconsciously reckoned it would be in a 38-43 degree inclined orbit like its predecessors. Indeed, the initial search elements we used were for a 43-degree orbit.

Second, this was an autumn launch and the very low orbital altitude means it is not well visible in wintertime from the Northern hemisphere, where almost all currently active satellite trackers are located. Almost all wintertime passes are in Earth shadow.

Now spring has arrived, OTV-5 is emerging out of these shadows, into the light. Weather has not been cooperating for me in the coastal area of the Netherlands where I am located so far, but I hope to be able to joing tracking this object soon. It is an interesting object to track, as previous OTV missions frequently manoeuvered between different orbital altitudes. Plus, the shuttle-like character of this object makes it a special one to track as well.

Sense and non-sense about the X37-B "Space Plane"

Quite some non-sense is appearing on the internet regarding the USAF's classified X-37B "Space Plane".



Most of this non-sense concerns the orbit of the X-37B and it's presumed extra "manoeuverability". Some typical examples can be found in the comments to this Slashdot coverage of the second X37-B flight (OTV-2), and I have seen similar misconceptions pop up in the comments to many other web-articles as well.


1. "Orbit targets Libya"

First: the claims that the current 43 degree inclination orbit for X37-B OTV-2 (and the 39 degree orbit for the previous OTV-1 mission) have been chosen to maximize coverage of a particular target, e.g. Libya. This "argument" stems from the difference with the more typical Polar orbit (60 to 90 degrees inclination) of reconnaissance satellites like the Keyholes and Lacrosses.

However: in terms of reconnaissance opportunities for any given location within the bounds of the orbital inclination, a 43 degree inclination orbit gives you no advantage over a polar orbit. On the contrary, while a polar orbit brings any latitude within reach for reconnaissance, a 43 degree orbit does not, as latitudes above 43 degree are less well covered (and far North or South latitudes aren't covered at all).

Note that for targets below 43 degree latitude, it really doesn't matter whether the satellite is in a 43 degree, 60 degree or 90 degree (polar) inclination orbit: all these orbits will bring such a target in reach, and the 43 degree orbit has no extra benefit compared to a 60 or 90 degree orbit at all in terms of target coverage.

Below diagram shows you the number of passes bringing Tripoli in range for 3 April 2011, for the X37-B as well as the KH-12 (polar orbit) and Lacrosse (57/67 degree orbit) satellites:



As can be clearly seen, the 43 degree inclined orbit of the X37-B does not result in many more passes compared to the other satellites in higher inclination orbits.

There is at best a marginal advantage over a true 90-degree polar orbit (the KH-12 Keyholes), but only marginal: and compared to the 57-67 degree orbits of the Lacrosses, the advantage in terms of number of passes over Libya is nil.

The maps below show the geographic coverage by a polar orbit (USA 186, a KH-12), a 57-degree orbit (Lacrosse 5) and the 43 degree orbit of the X37-B OTV-2. Limits of the geographic coverage of these satellites is indicated by the red lines: all locations inbetween these lines (the span of latitudes indicated by the red double arrow lines) get covered: where the limit is, is determined by the inclination of the orbit.

As the earth surface rotates beneath the orbital plane, strips of land get covered orbital cycle after orbital cycle. The X37-B does this in the same way as the other, "conventional" satellites.

Any given location inbetween the red lines on the X37-B map gets as well covered by the other satellite's higher inclination orbits: see also the previous diagram.









So it is nonsense to think that the 43 degree inclination orbit has been chosen to have a "better" look on a target near 43 degree latitude: a 90 or 60 degree inclination orbit will cover such a target just as well.

Instead, the 43 degree inclination has probably been chosen to maximize coverage of the X-37B orbit by US tracking and control facilities. So, it is a very prozaic explanation connected to the experimental nature of the craft, and the fact that it frequently re-boosts (it has to: it is in a low orbit and hence subject to quick decay).


2. "Manoeuverability"

Another frequent non-sensical remark about the X-37B is that it supposedly would be "more manoeuverable" than the typical reconnaissance satellite: and somehow able to "quickly get over a target" if necessary.

Again, this is a wrong view on how orbital dynamics and the dynamics of target coverage work. The X37-B might have wings and behave like an airplane in the atmosphere near landing: but in space, it is just a satellite subject to the same orbital laws as any other satellite. Like any satellite, it will cover any target within reach of the orbital inclination at least twice a day. And you just don't "steer" a spaceship to a target within an hour: it is not similar to flying an airplane (unlike suggestions in Battlestar Galactica or Star Wars). You change the orbital period and/or inclination and this determines when and how the satellite (X37-B in this case: but it is the same for any other satellite) will encounter a target, about twice a day (I say "about", because it actually concerns a number of passes centered on two times each day, 12 hours apart).

Below illustrations show this. The people who seem to think of the X37-B as a highly manoeuverable "plane" in space, are thinking along the lines of the first picture. That however, is not how it is! The second picture shows the true orbital movement of the X37-B, and as the pictures for Lacrosse 5 and USA 186 below that show, this is not different from the orbital movement of a "regular" reconnaissance satellite in any way:










Also take note of the fact that both on the previous mission and so far during this mission, the inclination of the X37-B orbit remains stable. It is not changing orbital plain repeatedly

The X37-B frequently makes small orbital maintenance manoeuvres (it has to, because of the quick rate of orbital decay at it's orbital altitude). Please note that, contrary to assumptions to the contrary often made, "conventional" reconnaissance satellites like the Keyholes and Lacrosses frequently manoeuvre as well. They have to, to maintain their orbital constellation, as zonal harmonics and atmospheric drag (even at their altitudes!) would quickly change their orbits otherwise, making them drift from the intended orbits.

Nothwithstanding this frequent manoeuvring (they do so multiple times a year) they stay operational for many, many years (Lacrosse 2 was finally de-orbited last week after being operational for 20 years, with very frequent manoeuvering during those 20 years).

So the X37-B doesn't really have much of an edge in sense of "manoeuverability" over any other satellite, contrary to what many people seem to think. The same in the sense of the benefits of "land and refuel" capabilities: other reconnaisance satellites operate many, many years including frequent manoeuvering.

The frequent manoeuvres the craft makes are manoeuvres to maintain orbital altitude and stay in a "frozen" orbit (an orbit that brings you over a target at the same time of the day, day after day, or each 2nd, 3rd or 4th day), and primarily this has to do with the low orbit (= high drag, high decay) the craft is in (this necessitates these frequent reboosts). It are not manoeuvres to change the orbit to quickly target new targets. That idea, is simply wrong and originates with people who have no clue about orbital dynamics in space.

The only real edge the X-37B has over other satellites is that it enables you to sent up and then retrieve payloads. For the rest, it cannot do anything more than any conventional satellite can do.