Fresh astro-underwear, anyone? Orbital shenanigans as Progress freighter has last-minute ISS docking wobble Hot on the heels of what the US alleged was an in-orbit "satellite killer" trial, Russia demonstrated it can still worry space station inhabitants with an eventful docking of its uncrewed Progress freighter. Those watching the video stream of the cargo ship docking with the International Space Station (ISS) were treated to the …
I guess it's down to the Russian rockets launching from Baikonur but it seems very strange that they only take 3 hours to reach the ISS and yet SpaceX takes much longer (about 19 hours - eg: Crew Demo 2 launched on 30 May 2020 at 19:22:45 UTC and soft docked at 14:16 UTC on 31 May 2020.
Baikonur is at 45.965°N 63.305°E and yet Kennedy is at 28°31′27″N 80°39′03″W.
Maybe it's down to the fact that rockets leaving Kennedy are normally launched towards the East over the Atlantic on a "just in case" basis? (and not "initially" flying over built up areas).
Can someone else can elucidate?
I'm not even sure if Kennedy Space Center has ever launched something going west, over central Florida. Maybe you could have done that in the 60s, but nowadays you have a major urban area at Orlando that you definitely would not want to drop space junk on.
I don't know about whether they take a lot of civilian payloads, but westbound military launches go out of Vandenberg AFB on the California coast, so you can shoot them out over the ocean.
The SpaceX crew Dragon deliberately went on a slow journey so the systems and habitability could be properly tested, in fact after the first launch attempt was aborted for weather the next opportunity was skipped because the flight would have been too short. Future Dragons may well take a quicker route if the timings are right.
All launches to the ISS from whatever launch site are timed to go up as the ground track of the ISS orbit passes over the launch site, but the ISS can be at any point along the orbit. This means the station and craft land up in the same plane but have to wait until the Soyuz/Dragon/Cygnus/Whatever catches up before they can dock. The different rockets can cope with different amounts of off ideal timing by doing a small (it costs fuel and payload) dogleg manouevre, and the latitude of Baikanour means the ground track gives a lot more flexibility in exact launch times when combined with the Soyuz capabilities. The Russians are thus able to pick launch times and dates to minimise the flight time, NASA and JAXA could pick launch dates that would give a 2 orbit 3 hour trip, but that would drastically reduce the number of possible launch windows.
Most space launches go to the east, so that the rotation of the Earth contributes to the velocity required to get into orbit. Launching to the west would require a lot more fuel to get to the same altitude.
As to why the different journey times, I would guess it really depends on the timing of the launch:
AIUI the ISS isn't in an equatorial orbit, but is skewed by about 50°, I believe as a compromise to make it easier for Russian launches to reach it. As a consequence of this, and it being in low orbit, the places its path crosses changes from one orbit to the next. Sometimes the station will be in a convenient place when your payload reaches orbit, sometimes you have to manoeuvre and wait for the orbits to sync up.
Clearly I'm an idiot... they fly up the *east* coast, not the west coast.
And yes the inclination is a compromise to make that, and the launch from soviet sites, reasonable.
It does mean that US launches actually don't ever get that far from land though (at least not until the abort option is "to orbit")
Yes, the "normal" Russian trajectory is just under 3 days, but that's a long time cooped up in a very tiny Soyuz.
They've spent a lot of time and effort getting an accurate launch, accurate tracking, and accurate correction burns. After launch they have a very short time to determine the trajectory and the appropriate correction, then do the correction. This took several years and 3 or 4 Progress missions before it was approved for manned Soyuz.
Things are launched east to take advantage of the Earth's rotational speed. it's WHY Kennedy is on the east coast.
The ISS is on an orbital inclination of 53 degrees. This is required to allow the Russians to play as their launch sites are further north than those available to NASA and ESA. When this was decided, it led to the program to reduce the Space Shuttles weight as it needed improved performance to be able to lift the payload to the required inclination. You will have all seen the pitch/roll well that is the important part of getting it on the right course. A note of trivia.. the OMS motors on the shuttle could only adjust its inclination by 3 degrees if you burn all of its available fuel.
The rest is a matter of orbital dynamics. In Demo2 case they were doing allot of checkout ahead of docking. Those who watched the approach and docking would have also noticed the series of checks done to confirm abort behaviors for docking.
So can you do a rapid ascent, yes, as long as the ISS is in the right place and you launch at the right time. Now if you had a shiny new ride I for one would like to take my time getting to where I needed to.
For those who want to try the last 2000ft you can with the SpaceX docking simulator here https://iss-sim.spacex.com
BvB
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"Those watching the video stream of the cargo ship docking with the International Space Station (ISS) were treated to the sight of the spacecraft seeming to go off course as it approached the outpost."
"RAMMING SPEED!"
Don't worry, that software bug is totally correctable.
CnC (Coffee and Cats) warning... (see icon)
perhaps the program needs a "chicken factor" (or 'pucker factor') built in - you know, when it would otherwise look like the automated spacecraft is "playing chicken" to an average sane observer, it does an early enough course correction to prevent navels (and anuses) from puckering up...
If my favorite pizza restaurant can institute contactless delivery, and call it progress, why shouldn't the Russian freighter do the same, particularly since its name is "Progress". The automated docking system was just trying to follow the latest coronavirus recommendations, until everyone started complaining.
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