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Looks like they nailed the launch: first stage recovered and Dragon 2 separated successfully. Congratulations SpaceX! Docking with the ISS is scheduled ~27 ho

Looks like they nailed the launch: first stage recovered and Dragon 2 separated successfully. Congratulations SpaceX! Docking with the ISS is scheduled ~27 hours from now on Sunday, March 3 at 10:55 UTC (5:55 EST). https://www.space.com/how-to-watch-spacex-crew-dragon-demo-1-mission.html https://www.space.com/how-to-watch-spacex-crew-dragon-demo-1...

labster 8y ago
Aw man, and I really wanted to binge watch this series. Well, at least this show moves faster than Orion.
jessriedel 8y ago
Anyone know why they choose a launch time and trajectory such that the arrival at ISS is more than a day later? It seems like you could choose to arrive at the ISS almost immediately after reaching orbital velocity if you wanted.
- sitharus 8y ago
  So they have time to validate the systems are working correctly. A direct launch would leave little margin for error, especially on a test flight. Edit: now I think more it also allows for variations in launch performance. Soyuz does a three day rendezvous as back when the system was designed the accuracy required wasn’t possible, though now they’ve planned a same-day docking.
  - JshWright 8y ago
    Soyuz has done "fast track" (same day) approaches for years now.
- azernik 8y ago
  tl;dr because the ISS orbit is not equatorial, choosing the right launch time is non-trivial and solutions are only approximate. ISS launch windows are complicated - you have to match both plane (i.e. the Earth needs to turn so that the Cape/Baikonur is under the ISS's orbit path) and phase (i.e. at the time the plane match happens, the station needs to be at the right part of its orbit for the spacecraft to meet the ISS right after launch). A launch site crosses the plane of the ISS orbit twice a day, but the phase angle at those crossings is often quite far off of optimal - you want the ISS to be a bit behind at launch so that by the time your spacecraft gets up to the right altitude/speed it's matched up. So you have to find the minimum phase angle at launch window for a targeted several weeks or so, then have the ISS make slight orbit changes to bring the phase angle closer to optimal. Once you're up and have as low of a phase-angle difference as possibly, you then have to spend a bunch of 90-ish-minute orbits getting your position in orbit matched up to the ISS. At fastest, you can get down to the single-digit-hours range, but that takes a good selection of launch window, a bit of a burn in advance from the ISS to tweak its phasing, tracking systems that don't waste an orbit determining where exactly you are, and no scrubs. This article is a good example of the process (but not the physics/geometry): https://www.nasaspaceflight.com/2018/07/progress-ms-09-super-fast-4-hour-rendezvous/ https://www.nasaspaceflight.com/2018/07/progress-ms-09-super... > The long sought attempt at launching a Russian Progress resupply vehicle to the International Space Station and having it rendezvous with the orbital complex after just two and a half orbits and just under 4 hours in space is being attempted. ... > As with the other fast track rendezvous attempts, the reboost and phasing alignment of the Space Station with the Baikonur Cosmodrome is only available for this launch day. A scrub to today’s instantaneous launch of Progress MS-09 would have resulted in the craft having to fly a two-day, 36 orbit phasing profile to the ISS on a realigned launch date later this week.
  - JshWright 8y ago
    If you don't mind me simplifying your answer a bit... Imagine the orbit of the ISS like a tilted hula hoop around the Earth, with the Earth revolving inside it. Because the Earth rotates once every 24 hours, any given spot on Earth will be directly underneath that hula hoop twice per day (once on either side of the hoop). When launching to the ISS, you need to launch when that orbit "hoop" is directly overhead. That's the bit that really matters, because you need to be in the same orbit. The ISS itself is almost certainly not overhead (it may be on the other side of the planet entirely), and so it will take some time to catch up to it.
- simonh 8y ago
  They don’t reach the stations orbital velocity immediately after launch though. What they do is launch into a lower orbit behind the station. Lower orbits have a shorter orbital period, so they gradually catch up and raise their orbit as they get closer. If the went into a ballistic trajectory directly at the station, there is a risk of debris from the launch, such as paint flecks, scraps of metal, etc hitting the station. Also a lower initial target orbit makes various abort scenarios easier. Then of course another poster has pointed out they need time to check and validate all the vehicles systems. Generally in space it’s best to avoid doing anything in a rush if you can avoid it. In recent years the Russians moved to a 6 hour launch to rendezvous window which is pretty quick really. This is what made it possible to capture footage of the launch from the station. https://youtu.be/ouBfzCgXHgk https://youtu.be/ouBfzCgXHgk
  - sandworm101 8y ago
    Technically they do reach the stations velocity. In fact they exceed it. The lower orbit is slightly faster. Total energy is lower, but they are moving faster than the station. A counterintuitive part of spaceflight is that often you have to first accellerate in order to slow down.
    - vermontdevil 8y ago
      Makes sense. Get up to a higher speed and it’s easier to do a controlled slow down. Than having to speed up after getting into orbit near another orbiting body.
      - JshWright 8y ago
        That's not really it. "Speeding up" and "slowing down" are equally easy (or hard). They're both acceleration, just in a different direction. The reason it's going faster is because it's lower. The lower an orbit, the faster the thing is moving. In order to slow down, you have to accelerate twice (I'm using the term "accelerate" here to refer to "going faster in the direction you're already going"). The first acceleration raises the far side of your orbit. You then have to "climb" up to that new higher orbit. Once there, you accelerate again to raise the low side of the orbit (otherwise you'd pick up all that speed again then "falling" back down to the lower altitude). At the end, you're in a new, higher, orbit, going slower than when you started.

labster 8y ago

Aw man, and I really wanted to binge watch this series. Well, at least this show moves faster than Orion.

jessriedel 8y ago

Anyone know why they choose a launch time and trajectory such that the arrival at ISS is more than a day later? It seems like you could choose to arrive at the ISS almost immediately after reaching orbital velocity if you wanted.

sitharus 8y ago
So they have time to validate the systems are working correctly. A direct launch would leave little margin for error, especially on a test flight. Edit: now I think more it also allows for variations in launch performance. Soyuz does a three day rendezvous as back when the system was designed the accuracy required wasn’t possible, though now they’ve planned a same-day docking.
- JshWright 8y ago
  Soyuz has done "fast track" (same day) approaches for years now.
azernik 8y ago
tl;dr because the ISS orbit is not equatorial, choosing the right launch time is non-trivial and solutions are only approximate. ISS launch windows are complicated - you have to match both plane (i.e. the Earth needs to turn so that the Cape/Baikonur is under the ISS's orbit path) and phase (i.e. at the time the plane match happens, the station needs to be at the right part of its orbit for the spacecraft to meet the ISS right after launch). A launch site crosses the plane of the ISS orbit twice a day, but the phase angle at those crossings is often quite far off of optimal - you want the ISS to be a bit behind at launch so that by the time your spacecraft gets up to the right altitude/speed it's matched up. So you have to find the minimum phase angle at launch window for a targeted several weeks or so, then have the ISS make slight orbit changes to bring the phase angle closer to optimal. Once you're up and have as low of a phase-angle difference as possibly, you then have to spend a bunch of 90-ish-minute orbits getting your position in orbit matched up to the ISS. At fastest, you can get down to the single-digit-hours range, but that takes a good selection of launch window, a bit of a burn in advance from the ISS to tweak its phasing, tracking systems that don't waste an orbit determining where exactly you are, and no scrubs. This article is a good example of the process (but not the physics/geometry): https://www.nasaspaceflight.com/2018/07/progress-ms-09-super-fast-4-hour-rendezvous/ https://www.nasaspaceflight.com/2018/07/progress-ms-09-super... > The long sought attempt at launching a Russian Progress resupply vehicle to the International Space Station and having it rendezvous with the orbital complex after just two and a half orbits and just under 4 hours in space is being attempted. ... > As with the other fast track rendezvous attempts, the reboost and phasing alignment of the Space Station with the Baikonur Cosmodrome is only available for this launch day. A scrub to today’s instantaneous launch of Progress MS-09 would have resulted in the craft having to fly a two-day, 36 orbit phasing profile to the ISS on a realigned launch date later this week.
- JshWright 8y ago
  If you don't mind me simplifying your answer a bit... Imagine the orbit of the ISS like a tilted hula hoop around the Earth, with the Earth revolving inside it. Because the Earth rotates once every 24 hours, any given spot on Earth will be directly underneath that hula hoop twice per day (once on either side of the hoop). When launching to the ISS, you need to launch when that orbit "hoop" is directly overhead. That's the bit that really matters, because you need to be in the same orbit. The ISS itself is almost certainly not overhead (it may be on the other side of the planet entirely), and so it will take some time to catch up to it.
simonh 8y ago
They don’t reach the stations orbital velocity immediately after launch though. What they do is launch into a lower orbit behind the station. Lower orbits have a shorter orbital period, so they gradually catch up and raise their orbit as they get closer. If the went into a ballistic trajectory directly at the station, there is a risk of debris from the launch, such as paint flecks, scraps of metal, etc hitting the station. Also a lower initial target orbit makes various abort scenarios easier. Then of course another poster has pointed out they need time to check and validate all the vehicles systems. Generally in space it’s best to avoid doing anything in a rush if you can avoid it. In recent years the Russians moved to a 6 hour launch to rendezvous window which is pretty quick really. This is what made it possible to capture footage of the launch from the station. https://youtu.be/ouBfzCgXHgk https://youtu.be/ouBfzCgXHgk
- sandworm101 8y ago
  Technically they do reach the stations velocity. In fact they exceed it. The lower orbit is slightly faster. Total energy is lower, but they are moving faster than the station. A counterintuitive part of spaceflight is that often you have to first accellerate in order to slow down.
  - vermontdevil 8y ago
    Makes sense. Get up to a higher speed and it’s easier to do a controlled slow down. Than having to speed up after getting into orbit near another orbiting body.
    - JshWright 8y ago
      That's not really it. "Speeding up" and "slowing down" are equally easy (or hard). They're both acceleration, just in a different direction. The reason it's going faster is because it's lower. The lower an orbit, the faster the thing is moving. In order to slow down, you have to accelerate twice (I'm using the term "accelerate" here to refer to "going faster in the direction you're already going"). The first acceleration raises the far side of your orbit. You then have to "climb" up to that new higher orbit. Once there, you accelerate again to raise the low side of the orbit (otherwise you'd pick up all that speed again then "falling" back down to the lower altitude). At the end, you're in a new, higher, orbit, going slower than when you started.