Quote from: DanielW on 07/11/2016 07:27 PMQuote from: Robotbeat on 07/11/2016 07:20 PMIt seems very unlikely that SpaceX would launch horizontally from Mars. Nor does horizontal engines on an upper stage make sense.You will have to help me on the basis for those assertions. With a thin martian atmosphere there would not be much penalty. Throttling would certainly have to be more responsive than vertical launching but that is not a known show stopper.You don't have horizontal engines on an upper stage. You have an upper stage that you are launching sideways. You just light the engines on one side of it slightly before the other and it rotates 90 degs. It makes as much sense as a swan dive maneuver on a landing craft.Except there's still a lot of drag for a second stage, especially one like the BFS (which probably stages fairly early).
Quote from: Robotbeat on 07/11/2016 07:20 PMIt seems very unlikely that SpaceX would launch horizontally from Mars. Nor does horizontal engines on an upper stage make sense.You will have to help me on the basis for those assertions. With a thin martian atmosphere there would not be much penalty. Throttling would certainly have to be more responsive than vertical launching but that is not a known show stopper.You don't have horizontal engines on an upper stage. You have an upper stage that you are launching sideways. You just light the engines on one side of it slightly before the other and it rotates 90 degs. It makes as much sense as a swan dive maneuver on a landing craft.
It seems very unlikely that SpaceX would launch horizontally from Mars. Nor does horizontal engines on an upper stage make sense.
Quote from: Robotbeat on 07/11/2016 07:30 PMQuote from: DanielW on 07/11/2016 07:27 PMQuote from: Robotbeat on 07/11/2016 07:20 PMIt seems very unlikely that SpaceX would launch horizontally from Mars. Nor does horizontal engines on an upper stage make sense.You will have to help me on the basis for those assertions. With a thin martian atmosphere there would not be much penalty. Throttling would certainly have to be more responsive than vertical launching but that is not a known show stopper.You don't have horizontal engines on an upper stage. You have an upper stage that you are launching sideways. You just light the engines on one side of it slightly before the other and it rotates 90 degs. It makes as much sense as a swan dive maneuver on a landing craft.Except there's still a lot of drag for a second stage, especially one like the BFS (which probably stages fairly early).The shuttle shape is going to be most aerodynamically stable in the reentry configuration, so launching from Mars (or after staging) horizontally would be like trying to fly a jet airplane backwards. Possible, perhaps, but definitely not ideal. Especially with those winglets.
Landing horizontally seems like a terrible idea, not at all SpaceX-y.DC-X demonstrated swan dive maneuver already. We don't need this horizontal landing nonsense.
The booster doesn't go to orbit, and there's no second stage so the shuttle must be it's own 2nd stage (confirmed by the trajectory graphic). At staging it's clearly pointed nose-downrange, but there are apparently no engines in the tail... so does it point it's dorsal side downrange and use belly engines? That seems questionable as there are still considerable aero loads at staging. Or do the engines pivot out and point back enough to continue vertically? There's no mechanism described for that.The booster clearly lands vertically, but I don't see any indication that the shuttle does.
Quote from: envy887 on 07/11/2016 03:13 PMThe booster doesn't go to orbit, and there's no second stage so the shuttle must be it's own 2nd stage (confirmed by the trajectory graphic). At staging it's clearly pointed nose-downrange, but there are apparently no engines in the tail... so does it point it's dorsal side downrange and use belly engines? That seems questionable as there are still considerable aero loads at staging. Or do the engines pivot out and point back enough to continue vertically? There's no mechanism described for that.The booster clearly lands vertically, but I don't see any indication that the shuttle does.Yes, at booster staging, the ship would need to pitch 90 degrees, open it's belly engine doors (which would need to be closed during launch for aerodynamics) and then begin thrusting up to LEO. Would probably need to be high enough so that any aerodynamic issues would be minimal for that. At that point it can keep the doors open for TMI. It would need to close them for Mars atmospheric entry, and then open them up again at terminal velocity to propulsively brake and then land. . They could stay open on the surface until launch, and stay open for TEI. They'd need to close again for Earth atmospheric entry, and then open again at terminal velocity for propulsive landing and braking.It also provides a pretty un-aerodynamic surface for Mars Launch like that. But maybe that's not too much of a problem in the thin Mars atmosphere? Not sure.
Quote from: envy887 on 07/11/2016 04:36 PMVertical landing after a ventral entry certainly seems feasible, that's not what I was questioning. I don't see any indication that Heidmann considered a vertical landing at all for this spaceship: all his articles show horizontal landings....Do we need a new thread for Heidmann's design? Because this thread is supposed to be about MCT, and it may get confusing if we're talking about a /specific/ (and fairly fleshed-out) speculation of someone's own imagining in a thread that's supposed to be about SpaceX's actual MCT.
Vertical landing after a ventral entry certainly seems feasible, that's not what I was questioning. I don't see any indication that Heidmann considered a vertical landing at all for this spaceship: all his articles show horizontal landings....
Have you read the title of the thread, it is indeed a SPECULATION thread,
Quote from: Impaler on 07/12/2016 12:19 AMHave you read the title of the thread, it is indeed a SPECULATION thread, It is supposed to be a MCT speculation thread. Not a generic speculation thread on just any Mars architecture. We have the Mars section for that. Things here should be based on what was said by SpaceX about MCT.
ISTM that accommodating two main load axis (for a 100 mT to Mars surface vehicle) that are perpendicular one to another is in severe conflict with SX known optimizations for PMF and cost. That alone seems to make the Heidmann (HCT) design off-topic for any MCT discussion, before even counting L2 info available (which further invalidates HCT as possible SX design). YMMV
I was simply suggesting that if we're starting to talk for several pages about one person's specific vision for what MCT is like, and if it's highly fleshed out, then it's probably best to have a dedicated thread. That doesn't mean it's off-topic here, but that it might be better in its own thread. Geez y'all.
...I don't see anyway that a super-dragon style capsule will get enough drag to slow down enough. ...
I was simply suggesting that if we're starting to talk for several pages about one person's specific vision for what MCT is like, and if it's highly fleshed out, then it's probably best to have a dedicated thread. That doesn't mean it's off-topic here, but that it might be better in its own thread.
Quote from: DanielW on 07/12/2016 01:13 PM...I don't see anyway that a super-dragon style capsule will get enough drag to slow down enough. ...If Red Dragon works, a larger vehicle with the same entry velocity, lift/drag ratio, ballistic coefficient, propellant mass fraction, and engine efficiency should work just as well. Because of the cube-square law it will have to be less dense, but since it's largely made of nearly empty propellant tanks that shouldn't be a major issue.Trading propellant mass for engine efficiency (Raptor 380s vs. SuperDraco 240s) also helps hit the required density reduction.
Yes, but -- how wide would such a scaled-up Dragon capsule be at the base, if it's got to be designed to carry at least 100 people, along with all the stuff (like food, water and life support) they will need for three to six months?I think simply scaling up the dimensions of a Dragon to where it has the interior space available for the actual stated mission requirements would make the base diameter in the hundreds of meters. How ya gonna fit that on any booster, much less one with the most-commonly-speculated (see L2) width of the BFR?And if you change the basic shape, you inevitably have to go through a lot of design work to achieve similar lift/drag characteristics, etc. In other words, BFS is gonna have to be designed from scratch, it won't take advantage of Dragon's shape or flying characteristics as a starting point.
Mars Colonisation Transportation: Project Revelation Before Rumours
But a noise is that SpaceX would work on a Raptor 700 Tf !
One interesting tidbit, though:QuoteBut a noise is that SpaceX would work on a Raptor 700 Tf !Not sure of rumor source for an F-1 class engine, but certainly would simplify first stage design if nine 1.5-1.6Mlbf engines were used on booster.