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USAF Missions


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2017 May 27
Saturday, Day 147

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Jumping Beans - OTV Launch Windows

With launch of the third OTV mission when the first of the USAF/Boeing X-37B space planes made its second journey into space, evidence was emerging that the X-37B's launch windows are dictated by the location in space of another satellite, already in orbit.

Across the three launches, an apparently inconsistent pattern of launch windows and launch times has surfaced. They point to the possibility of the X-37B being imaged soon after launch by a reconnaissance satellite.


Why Imaging?

Inspection is reminiscent of the post-Columbia space shuttle era when cameras were used by STS crews to check the tiled areas for damage once in orbit. There is a difference between STS and OTV missions in that OTV is launched on top, rather than the side of, a rocket stack. For the critical part of the flight through the lower atmosphere, it is inside a protective shroud so is not exposed to the air flow and should be safe from the sorts of events that used to hit the shuttle.

Vibration is, however, a factor and in the event something should be damaged, there is no crew aboard to wield a camera. Overall condition of the vehicle's exterior is about the only thing than can't be measured by a sensor and sent back as telemetry, hence the need for a remote look.

First - why is there a need to develop a habit of inspecting an orbiting spacecraft anyway? The answer lies in Project Management. With the risk that the thermal insulation could be damaged during launch and lead to the vehicle being lost on re-entry then, with mission likely to be 1-2 years in duration, it's a long time to wait before finding out.

By inspecting it right at the start, if something points to the vehicle not making it back to Earth then planning for building its successor can start earlier rather than later. It may lead to the mission being managed in a different way if it is known that the craft will never be retrieved. There's also avoidance of the embarrassment factor. It can be ditched in the deep Ocean rather than unexpectedly showering Californian coastal waters with re-entry debris!


Clues

Information can be gleaned from the pattern of change in planned lift off time from day to day when launches have to be delayed. For the majority of launches, the time either stays the same or drifts by a uniform daily amount. Drift can be driven by on-orbit solar lighting angles, or the need to align the orbit position with those of satellites in the same constellation already in space.

In the case of OTV, potential launch times have jumped around from day to day suggesting that something more than the usual influences are at work. These are some of the times published for OTV launch windows over the years:

Date Window 1
(UTC)
Duration Window 2
(UTC)
Duration Window 3
(UTC)
Duration
USA 212/Mission 12010 Apr 2022:46144 minutesincl
USA 212/Mission 12010 Apr 2122:44143 minutesincl
USA 212/Mission 12010 Apr 2223:5210 minutes
USA 226/Mission 22011 Mar 420:392 hoursincl
USA 226/Mission 22011 Mar 521:0910 minutes22:4610 minutes
USA 240/Mission 32012 Dec 1118:033+ hoursinclincl
USA 240/Mission 32012 Dec 1217:003+ hoursinclincl


A Different View

The change in the structure of the Mission 2 launch window between 2011 Mar 4 and Mar 5 suggests that all of the longer (2+ hours) windows hide two short windows within them. Using the way the Mar 5 window splits up allows an estimate of what the other windows look like in reality. Note - the Mission 1 windows run across midnight into the following day.

The 'window within a window' format was again confirmed during the ULA Launch webcast covering the final minutes of the Mission 3 countdown. Three launch windows were given for each of Dec 11 and Dec 12:

Date Window 1
(UTC)
Duration Window 2
(UTC)
Duration Window 3
(UTC)
Duration
USA 212/Mission 12010 Apr 2022:4610 minutes00:2310 minutes
USA 212/Mission 12010 Apr 2123:1910 minutes00:5610 minutes
USA 212/Mission 12010 Apr 2223:5210 minutes01:2910 minutes
USA 226/Mission 22011 Mar 420:3910 minutes22:1610 minutes
USA 226/Mission 22011 Mar 521:0910 minutes22:4610 minutes
USA 240/Mission 32012 Dec 1118:0310 minutes19:4010 minutes21:1810 Minutes
USA 240/Mission 32012 Dec 1217:0010 minutes18:3710 minutes20:1510 Minutes

The pattern seems to be that a time for a launch opportunity on any particular day is fixed and the time for the next day is 30-33 minutes later. After three such steps, the time jumps back by about 90-96 minutes.


Behind The Times

Taken together, all the launch window times suggest that there is an underlying cycle time of 96-98 minutes, and that is what drove thinking towards a link with an already-orbiting satellite, or satellites. A candidate that fits the bill is the KH-11 constellation of imaging satellites as they have orbital periods of the right sort of value.

The intervals between OTV windows on a particular day are to ensure that that the OTV and the KH-11 arrive their orbit crossing point simultaneously. The daily drift is to allow for the fact that the KH-11 complete an whole number of circuits in about 24.5 hours.

The KH-11 factor also dictates the period in day when a launch must occur because the X-37B has to be suitably illuminated for a photograph to be taken. The published launch windows point to the period being limited to less than two hours centred around 22:30 UTC.


Background

The possibility of KH-11 involvement was raised at the time of Mission 2 in two postings to the Seesat-L discussion group: http://satobs.org/seesat/Mar-2011/0076.html and http://satobs.org/seesat/Mar-2011/0084.html

A related note in connection with Mission 3 also appears on Seesat-L:
http://www.satobs.org/seesat/Dec-2012/0079.html

Launch and orbit notes for the three missions are extracted from the annual launch diaries:

2010-015
Atlas V 501, AV-012
Cape Canaveral AFS, Florida, USA
2010 Apr 22, 23:52
USA 212 (X-37B/OTV-1 Flight 1)
2010-015A
36514
Re-entered or landed - 2010 Dec 3
First flight of the USAF Boeing-built X-37B space plane. Launched at the beginning of a 4 hr launch window. Landed Vandenberg runway 2010 Dec 3 with wheel stop at 09:16:02 UTC. Launch delayed from April 20. The X-37B was removed from the Shuttle launch manifest following Columbia's destruction. Orbital elements not released by Spacetrack so parameters are based on amateur observation.

epoch (UTC)         
s-m axis
( km )
ecc    perigee
( km )
apogee
( km )
period
( min )
incl 
( ° )
ω  
( ° )
2010 Jun 1, 20:2967870.001539941992.7439.99294
2010 Aug 30, 08:5968140.000743144193.3039.9953
2010 Nov 29, 04:2666610.000627928790.1740.0033

2011-010
Atlas V 501, AV-026
Cape Canaveral AFS, Florida, USA
2011 Mar 5, 22:46
USA 226 (X-37B/OTV-2 Flight 1)
2011-010A
37375
Re-entered or landed - 2012 Jun 16
Second X-37B space plane - making its first flight. A mission by the first X-37B flight model was undertaken during 2010 and this second flight will refine some of the tests that it undertook. Mission originally planned for 270 days to Nov 30 but, on that day, USAF announced an indefinite extension. 2012 May 30 - USAF let it be known that the X-37B will return to Vandenberg AFB during tthe first two weeks of June, it landed 2012 Jun 16 at 12:48 UTC. Orbital elements not released by Spacetrack so parameters are based on amateur observation.

epoch (UTC)         
s-m axis
( km )
ecc    perigee
( km )
apogee
( km )
period
( min )
incl 
( ° )
ω  
( ° )
2011 Mar 30, 03:1367070.001232133791.1142.81148
2011 Nov 27, 18:2167130.001432534491.2242.7614
2012 Jan 7, 21:2167130.001032834191.2242.7819
2012 May 18, 02:0966620.002826530290.1942.80208

2012-071
Atlas V 501, AV-034
Cape Canaveral AFS, Florida, USA
2012 Dec 11, 00:11
USA 240 (X-37B/OTV-1 Flight 2)
2012-071A
39025
Re-entered or landed - 2014 Oct 17
Second flight of the first model of the USAF/Boeing X-37B space plane. Detailed payload and mission purpose are unknown. Launch by United Launch Alliance an behalf of USAF Rapid Capabilities Office. Launch vehicle upper stage re-entered over the Indian Ocean during the first circuit of the Earth. The first orbit listed is an estimate by Ted Molczan based on observations from Cape Town by Greg Roberts soon after launch. Landed on the runway at Vandenberg AFB 2014 Oct 17 at 16:24 UTC.

epoch (UTC)         
s-m axis
( km )
ecc    perigee
( km )
apogee
( km )
period
( min )
incl 
( ° )
ω  
( ° )
2012 Dec 12, 18:0067280.001234235891.5443.50327
2013 Mar 6, 00:3667750.000539340092.4943.64112
2014 Jul 22, 07:5467290.002033736591.5643.51324


Page date: 2012 Dec 11
Updated: 2014 Oct 12
Updated: 2015 Dec 20

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