Quote from: charliem on 06/12/2012 10:20 pm- As we know Dragon needs to prove a number of its [yet] theoretical capabilities, but my personal impression about the Nasa personnel doing the presentations is that they are non as skeptical as some over here ... Interesting, so Dragon can manage a re-entry through a CO2 atmosphere? I wonder how cost effective it is compared to standard entry options such as MSL.
- As we know Dragon needs to prove a number of its [yet] theoretical capabilities, but my personal impression about the Nasa personnel doing the presentations is that they are non as skeptical as some over here ...
According to Mueller, SpaceX’s material, called PICA-X, is 10 times less expensive than the original, “and the stuff we made actually was better.”
Interesting, so Dragon can manage a re-entry through a CO2 atmosphere? I wonder how cost effective it is compared to standard entry options such as MSL. Pity that it's limited to only 1mT, but it's a stepping stone to a large manned Mars lander.
Quote from: charliem on 06/13/2012 03:29 amQuote from: charliem on 06/13/2012 02:36 amSo the Dragon capsule has to start its SuperDraco engines at ~550 m/s, 800 m before crashing, and decelerate at 7 g ... what a ride!!Those numbers can't be right. I've rechecked them against the presentation and this time it's not my mistake.In one of the slides we can read: "* Performs a direct transition to powered flight at Mach 2.24 800 m above ground utilizing SuperDraco thrusters".That speed can't be vertical, because then a simple v=sqr(2.h.a) says that the minimum distance to brake from 550 m/s to zero at 7 gees is 2200 meters, so the only possibility that remains is a very very shallow descent.+1, there's an inconsistency somewhere. Forgetting about gravity, that works out to be about a 70 degree angle.
Quote from: charliem on 06/13/2012 02:36 amSo the Dragon capsule has to start its SuperDraco engines at ~550 m/s, 800 m before crashing, and decelerate at 7 g ... what a ride!!Those numbers can't be right. I've rechecked them against the presentation and this time it's not my mistake.In one of the slides we can read: "* Performs a direct transition to powered flight at Mach 2.24 800 m above ground utilizing SuperDraco thrusters".That speed can't be vertical, because then a simple v=sqr(2.h.a) says that the minimum distance to brake from 550 m/s to zero at 7 gees is 2200 meters, so the only possibility that remains is a very very shallow descent.
So the Dragon capsule has to start its SuperDraco engines at ~550 m/s, 800 m before crashing, and decelerate at 7 g ... what a ride!!
Could they have meant 800m above the datum, which would mean landing 1400m below the datum.Add in some constant velocity descent (which was mentioned) and we have a landing at about 1500m below the datum.
Quote from: MikeAtkinson on 06/14/2012 07:11 pmCould they have meant 800m above the datum, which would mean landing 1400m below the datum.Add in some constant velocity descent (which was mentioned) and we have a landing at about 1500m below the datum.The written paragraph is clear: "800 m above ground" (sic).And it's not necessary after all.I've done some more math. It seems that indeed the flight path of a Dragon would be really flat, under 20 degrees while crossing the 0 altitude MOLA reference.You can see it in this graphic for the entry path: http://forum.nasaspaceflight.com/index.php?action=dlattach;topic=28668.0;attach=392917Vertical and horizontal scales are very different. Once you compensate for that it's evident how shallow the whole trajectory is. Quite different that an earth reentry.Following that path 2,200 meters ahead on the final approach mean only about 500 or 600 of descent.