According to this article, Russia recently tested a new launch trajectory that shaved over 45 hours off their normal flight time.

What allowed for this difference? Doesn't it seem like the shortest distance will be the closest thing to a straight line?

  • $\begingroup$ An interesting consequence is that on the 2 day orbit, the cosmonauts have time to get out of the seats, out of the suits, clean up, and then back in for docking. In the new version they have to stay in their seats the whole time, and it is reportedly very uncomfortable. (Ever see the video of how they strap their legs in? Tied in tight) $\endgroup$
    – geoffc
    Jul 19 '13 at 4:44

The main difference between the two options is that the amount of time is cut down for orbital correction maneuvers. Essentially, a docking maneuver looks something like this:

  1. Launch the vehicle to an almost identical, but not quite identical, orbit to the desired object.
  2. Very carefully identify the orbit you are in, and the orbit you want to get to. Do this somewhat far away, to ensure no collision.
  3. Maneuver your spacecraft to be just above the space station. This will have you slowly approaching the station.
  4. Match the speed when you just barely reach the station.

The main difference is that there was more time spent in the second step, and the original launch was quite a bit further away.

Just to give you an idea, the Dragon approach looks something like this.

  1. Launch into an insertion orbit, with the perigee around 200 km, and the apogee around the space station altitude (But slightly lower).
  2. Check out systems
  3. Raise the orbit to be slightly above the space station. This takes at least 2 burns, spaced an hour apart.
  4. Match the speed at the correct time.

The main difference is that the spacecraft is launched deliberately in to an insertion orbit. However, this gives the spacecraft more opportunity to correct for mistakes.

  • 4
    $\begingroup$ I don't think any visiting vehicles use a rendezvous orbit that's "slightly above the station". They use an R-bar approach from below the station. $\endgroup$ Oct 16 '14 at 19:50

They have shaved off 45 hours, not minutes.

It seems to be a whole complex of factors:

After the Space Shuttle retirement, the ISS orbit could be raised to provide better ballistic possibilities.

The new on-board computer allows to conduct ballistic calculations faster and with less dependence on ground control.

The orbit measurements precision has improved over time.

The communication has improved over time, going through the station and satellites.

There was a constant pressure from the cosmonauts themselves, because one gets very sick during the two days scheme.

While the sequence of events is now denser and the ballistic gaps are narrower, they always have a backup variant to go by 2 days scheme.

Altogether it made the new scheme possible, and they promise to bring it down to four and even two hour scheme.

This answer is based on two interviews given by Rafail Murtazin the deputy head of Energia ballistics department, and by Sergey Krikalev the head of the Yuri Gagarin Cosmonauts Training Center.

  • $\begingroup$ Wow! Amazing. 45 Hours! $\endgroup$
    – Undo
    Jul 19 '13 at 2:18
  • $\begingroup$ Ah! There is an english translation of Murtazin's interview. Here: gagarin.energia.ru/… $\endgroup$
    – horsh
    Jul 19 '13 at 2:20
  • $\begingroup$ Funny, (OMG!) the "google translate" translates "the head of the Yuri Gagarin Cosmonauts Training Center Sergey Krikalev" (that is "глава Центра подготовки космонавтов Сергей Крикалев") as "the head of the Cosmonaut Training Center Esther Dyson". Beware. $\endgroup$
    – horsh
    Jul 19 '13 at 9:55
  • 2
    $\begingroup$ For what it's worth, the way they're able to cut down so much on the time is that they choose a lower phasing orbit than usual, which results in a higher drift/closing rate between the Soyuz and the ISS. $\endgroup$
    – user29
    Jul 19 '13 at 13:08
  • $\begingroup$ Can be improved further by including drawings from Murtazin's presentation in the linked interview. $\endgroup$ May 9 '14 at 0:37

The difference is that the phasing delay is eliminated with the help of ISS maneuvers and a more precise path can be flown by updated flight computers.

Imagine a "normal" launch, such as the shuttle might have used from Florida. When you get to orbit, small changes in altitude are fairly easy to accomplish, but inclination changes are very expensive. In order to reach the station, the shuttle waits until the earth's rotation takes it just about underneath the orbit. During a small window it then launches into the same inclination.

At the time of launch, the station may be at any point along the orbit path. The difference between the station's location and the shuttle's location is the phase difference. To conserve fuel, the shuttle isn't going to fly above the station and then descend back, so all of the difference has to be made up by flying lower than the station. This gives only a relatively small altitude range between the two. This difference is sufficient to allow the shuttle to reach the station within 3 days no matter the phase. When the phase is correct, the shuttle can begin the approach.

You can imagine that having the ISS at one particular point in the orbit would allow for the approach to the station to happen immediately. The trick is how to launch when that is the case.

The big thing for the fast approach profile is that the launch is planned well in advance and the ISS is maneuvered to the correct point. This allows the phase to be within limits at the time of launch. Moving the ISS is expensive, so this is only done for crewed flights now. Cargo can wait it out. The article below points out that updated flight control systems were also necessary. The profile requires that the craft perform burns outside the range of ground stations, and that wasn't possible on previous versions.



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