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Launches and Orbital Operations


Tyneside, UK
2021 Feb 26
Friday, Day 57

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OTV-5 Rideshare


track map


Background

Boeing's X-37B re-usable spaceraft was launched on its fifth mission 2017 Sep 7. As far as the world was concerned, the Falcon 9 rocket placed a single payload into orbit. All that could be gleaned at the time was available from navigation warning notices issued for the ground track out of Florida and for the subsequent forced re-entry of the Falcon 9 upper stage above the Indian Ocean about four hours after lift-off.

The Indian Ocean navigation warnings showed the Falcon 9 upper stage re-entering from an orbit inclined at 63° indicating that it made a significant plane change between releasing the X-37B and hitting the atmosphere.

When the X-37B landed 2019 October 27 after two years in space, the announcement summarising the mission included the phrase "as well as providing a rideshare for small satellites". No details were provided of the satellites.

Many pundits simply assumed that the satellites has been released from the X-37B although some thought otherwise. Why use up valuable cargo-return space inside the vehicle with something not intended to be brought back to Earth?

It was more likely that the satellites were attached to some other structure on the launch vehicle, an explanation enhanced by the description of a "rideshare" which is usually applied to something carried alongside a main payload rather than being part of it.

The SpaceX Transporter 1 launch 2021 January placed more than 140 payloads into orbit. One of the payload dispensers was a Maverick Space Systems' deployer mounted on the rear bulkhead of the Falcon 9 second stage near the engine. It released three 1U cubesats into orbit. A similar system could have been carried on the OTV-5 launch.

There is a summary of the launch and its payloads in the list of launches for 2017 on the zarya.info website.


Space Catalogue 2020

2020 February 11, three new satellites appeared in the catalogue published by Space-Track. They were given the first available NORAD Catalogue Numbers at the time but were designated as objects from the OTV-5 launch, and given the next available names in the "USA" satellite series. The payloads were said to be "no longer in orbit" indicating that natural decay of the orbit through air drag had caused them to re-enter the atmosphere by that time.

It may be that the USA realised belatedly that it had a legal obligation to register them under international treaties. It is similarly possible that acknowledment of the satellites' existence had been held back until they had all re-entered the atmosphere.

Early in 2001, the United Nations published the space launch summary that the US had submitted in June of 2020. It included the three satellites from the OTV launch.


Orbits

The UN document lists the satellites in an orbit of 182 x 356 kilometres at 56°.9 inclination - a copy of the relevant page from the submission is at the top of this web page.

The figures are the same as the ones provided to the UN in relation to OTV-5 itself. What the numbers may represent is the initial orbit of the Falcon 9. The zones covered by navigation warnings indicate that the Falcon 9 departed on a trajectory that would have put the X-37B into an orbit at 45° inclination. About six months later, amateur observers found the X-37B in a circular orbit near 350 kilometres and inclined at 54°.5, close to the 56°.9 of the UN documents.

Navigation warnings for the US east coast indicated an initial track out of the Kennedy Space Center at about 43° inclination but the upper stage probably then steered north to follow a curved ground track put the X-37B into an orbit inclined at 55°-57°. Direct launch from Florida to that inclination would have involved passing close to the US east coast and overflying Newfoundland and Nova Scotia. From the 182 x 356 km orbit a second firing of the Falcon 9 engine would have circularised it at 356 km.

The Falcon 9 engine was later re-ignited to change the inclination to 63° and then cause re-entry above the southern Indian Ocean.

Given that the prime mission of the launch was to orbit the X-37B, release of the Cubesats probably came after the X-37B had departed but before the manoeuvre to 63° so they too probably ended up at about 350 km in a circular orbit.


North Atlantic Navigation Warning



Indian Ocean Navigation Warning


Page date: 2021 Feb 6

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