Will SpaceX try the fast-track route to the ISS as the Russians?
Quote from: phillipdoug on 02/06/2015 01:37 amWill SpaceX try the fast-track route to the ISS as the Russians?I can't find the reference, but I recall Hans Koenigsmann responding to a question at a NASA presser that SpaceX would use the 6 hour flight plan with crew.
SpaceflightNow has posted a timeline for the DSCOVR launch. Among the images, the one for the jettison of the fairing is particularly interesting. It appears to be from the first stage. Is this a photo from the first stage, from a ground asset, or a simulation?
Quote from: mme on 02/06/2015 02:06 amQuote from: phillipdoug on 02/06/2015 01:37 amWill SpaceX try the fast-track route to the ISS as the Russians?I can't find the reference, but I recall Hans Koenigsmann responding to a question at a NASA presser that SpaceX would use the 6 hour flight plan with crew.Yeah, I remember that, too. He claimed that Dragon 1 was already technically capable of doing fast rendezvous, but fast rendezvous requires thruster burns on the ISS side as well and NASA saw no need to waste ISS propellant when it's only cargo going up.
Quote from: cscott on 02/06/2015 07:44 amQuote from: mme on 02/06/2015 02:06 amQuote from: phillipdoug on 02/06/2015 01:37 amWill SpaceX try the fast-track route to the ISS as the Russians?I can't find the reference, but I recall Hans Koenigsmann responding to a question at a NASA presser that SpaceX would use the 6 hour flight plan with crew.Yeah, I remember that, too. He claimed that Dragon 1 was already technically capable of doing fast rendezvous, but fast rendezvous requires thruster burns on the ISS side as well and NASA saw no need to waste ISS propellant when it's only cargo going up.Wow, you wouldn't think that the relatively puny thrusters on the 450mT ISS could make that much of a difference for a rendezvous in such a short period of time.
Quote from: Coastal Ron on 02/12/2015 08:08 pmWow, you wouldn't think that the relatively puny thrusters on the 450mT ISS could make that much of a difference for a rendezvous in such a short period of time.They Dont!There's a launch opportunity ~once a day to reach the ISS on a slow rendezvous - the ISS just has to be in the same plane as the launch site at the instant of launch, but you don't care much WHERE it is on the plane (even on the other side of the earth) since the dragon can drift 'along' that plane over a few days by being in a slightly higher or lower orbit.But, if you want a fast rendezvous, the ISS has to be in the same plane, and effectively at the same position as the dragon once it reaches orbit. (visualise the ISS as in plane, and also nearly over, the launch pad at the moment of launch) This occurs very rarely under normal operations. So, it has to be set up days in advance, by first raising and lowering the ISS's orbit, and letting the ISS do the drifting, towards or away, along the plane, from where the dragon is expected to be when it reaches orbit. That takes a fair bit of fuel and planning, and if the falcon scrubs, its all for naught. And then you have to lower/raise the whole station again!They do it for soyuz spacecraft launches, since they have human cargo, cramped in a tiny can, and the soyuz has a damn good on-time launch record!
Wow, you wouldn't think that the relatively puny thrusters on the 450mT ISS could make that much of a difference for a rendezvous in such a short period of time.
Great explanation. Apparently the Soyuz and it's carrier rocket don't have enough extra maneuvering capability, so the ISS has to "help". I wonder if the Dragon and CST-100 will have enough maneuvering capability to reach the ISS without the ISS needing to help?
Quote from: Coastal Ron on 02/12/2015 09:07 pmGreat explanation. Apparently the Soyuz and it's carrier rocket don't have enough extra maneuvering capability, so the ISS has to "help". I wonder if the Dragon and CST-100 will have enough maneuvering capability to reach the ISS without the ISS needing to help?They would have plenty of fuel/ delta-v to rendezvous, but only if you wish to spend several days phasing on orbit!If the two craft are in plane, and at approx the same ISS altitude , but completely out of phase (i.e. on opposite sides of the earth), then effectively they are 45 mins apart.To catch up (or fall back), over the course of 2 days, at one orbit every ~90 mins (or 16 orbits a day), thats only 1.5 mins per orbit.But, if you try to do it fast, in less time/orbits, you will need such a high or low intermediate orbit that the fuel burned to go up and back down again would be excessive, or else you're so low you'd re-enter.And, more importantly, you would sort-of end up 'alongside' the ISS at the end of your maneuvers, but in a different plane, orbiting parallel to it, but way off to the side, and a plane change is very expensive in delta-v. (you can't just thrust 'across', like jumping from one train to another on parallel tracks, since that would effectively be an inclination change)
Hey gang,Anybody know how F9 second stage does ullage?A friend asked and I realized I didn't know...thanks
[...I'm getting better educated on this. So are you saying that even if the Falcon 9 2nd stage was loaded up with more propellant and was able to do more maneuvering burns in orbit with the Dragon still attached (assuming that didn't rip the solar panels off of the Dragon), that it still wouldn't be enough to do a fast rendezvous with no ISS engine burns?
...No doubt there is some amount of energy an approaching vehicle can use to do the fast approach on their own, but the question is whether either of the Commercial Crew vehicles and their carrier rockets would have that much energy available to use?
http://www.wsj.com/articles/BL-DGB-40041QuoteSpaceX’s Valuation Rockets to $12 Billion With Google InvestmentSpaceX now ranks fourth on The Wall Street Journal’s list of billion-dollar private companies, securing a $12 billion valuation.>
SpaceX’s Valuation Rockets to $12 Billion With Google InvestmentSpaceX now ranks fourth on The Wall Street Journal’s list of billion-dollar private companies, securing a $12 billion valuation.>