# ISS location identification; estimate size and direction of astronaut acceleration puzzler

note: This question addresses the same video and phenomenon described in this answer (which I found after posting this) but here I'm asking for an analysis of the trajectories of the test masses (the astronauts) based on known ISS structure, not accelerations read from sentences in blogposts.

The NASA Johnson YouTube video Space Station Reboost: The Inside Story shows Expedition 29 Flight Engineer Satoshi Furukawa in orbit around the Earth, inside the ISS during a propulsive orbit-boosting maneuver. From the camera's perspective Furukawa appears to be accelerating away from the camera, but it's really the ISS changing velocity.

Furukawa's position changes substantially during the video, accelerating from one module to the next.

Two questions:

1. In which direction does Furukawa accelerate; towards the front or the back, and why?
2. Roughly how fast does Furukawa accelerate? I've included two screenshots separated by about 28 seconds, if the distance were 5 meters for example, that would be about 0.013 m/s^2. This requires identification of the two locations and estimating the separation. Here's an excellent ISS Virtual Tour to navigate around and estimate distances.

• There's code golf already, maybe we should at least get a space-golf tag for puzzler type questions?
– uhoh
Mar 8, 2019 at 15:51
• Here's a different boost maneuver video just fyi youtu.be/5tcuKI3-B70?t=274
– uhoh
Mar 11, 2019 at 2:08
• I'm not answering the full question, but the camera is at the front of Node 2, looking backward through N2 into the Lab. Mar 11, 2019 at 15:31
• I don't think space-golf would be good. x-golf implies the fewest possible strokes (or characters/bytes in PPCG) so it would imply answering your question in the least amount of words possible hehe. Maybe calculation or space-puzzle. Mar 11, 2019 at 19:16
• If iss is accelerating, that would be a prograde or retrograde boost, wouldn’t it? I imagine it would most likely need prograde boosts because drag leads to orbital decay.
– Paul
Mar 12, 2019 at 0:46

They float from Node 2 (Harmony) into the Destiny module - so towards 'aft' of the station. That means the station is propelled from the rear - either by thrusters installed in the Zvezda module or by a Progress spacecraft docked to the rear-most port of Zvezda. (obviously the thrusters are directed 'away' from the station not to spray it with hydrazine, so aft thrusters propel it 'bow forward').

Using proportions on some images with dimensions of ISS I estimated the distance (e.g. this ) - starting at the edge of entrances into Columbus and Kibo from Harmony, to about middle of Destiny (it's hard to spot where exactly Furukawa stops but about mid-way should be correct considering both the time of him floating through the module and the astronaut behind him going from Node 1) - 7 meters. (566px = 357ft = 108.81m ; 37px = ~7m)

The time in the video is about 28-29s.

Using the uniformly accelerated motion calculator we're getting 0.017 m/s^2.

It seems my distance estimate matches that of Rhett Allain who used angular size of the astronauts although I can't get where in the world he got the time from...

• Wouldn’t propulsion “from the rear” indicate a prograde thrust maneuver? Or are these modules not aligned with the direction of the space station’s motion?
– Paul
Mar 12, 2019 at 13:02
• @paul: They are, and that's a prograde thrust maneuver - but reboosts will be always prograde, to raise the orbit, but with a bow-mounted retro-thruster propulsion module, the station could just turn aft-prograde and burn the retro-thrusters to accelerate. That alignment is convenience, not necessity.
– SF.
Mar 12, 2019 at 13:10
• Oh, several surprises! 1) Rhett Allain writes better stuff than his WIred blog; that's great to know! 2) Rhett Allain already did this. I know he has described some software that does metrology or photogrametry to videos in some of his posts, but that curve looks incredibly smooth for a rotating person.
– uhoh
Mar 12, 2019 at 13:18
• Your estimate agrees fairly well with the thrust of the Zvezda module (~5.9kN) divided by the mass of the station in late 2011 (417 tons), yielding 0.014 m/s^2. Mar 12, 2019 at 21:54