Author Topic: MCT Speculation and Discussion Thread 4  (Read 605626 times)

Offline jpo234

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Re: MCT Speculation and Discussion Thread 4
« Reply #2380 on: 07/11/2016 02:43 PM »
Where does it show a vertical landing? He seems rather stuck on the horizontal landing, and there are no engines in the rear of that thing in the illustrations.

It doesn't show a vertical landing. But since it doesn't have anything but a big heat shield on the side I'm assuming a vertical landing. I might be wrong, happened before.

Which makes me wonder... how does it get to orbit? Horizontally?

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« Last Edit: 07/11/2016 02:45 PM by jpo234 »
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Re: MCT Speculation and Discussion Thread 4
« Reply #2381 on: 07/11/2016 03:04 PM »
It does land horizontal, see pictures at the bottom of this page
http://planete-mars.com/mars-colonization-transport-main-findings-of-our-analysis/


Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2382 on: 07/11/2016 03:11 PM »
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.
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Online envy887

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Re: MCT Speculation and Discussion Thread 4
« Reply #2383 on: 07/11/2016 03:13 PM »
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.

Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2384 on: 07/11/2016 04:24 PM »
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.

See SpaceX's old reuse video. Shows the upper stage reentering on its belly, then at some point it transitions and in the end it lands vertically:


That counts as some indication (hint), although we do not have any actual source info that says it will land vertically (and it could be that they were or are still trading how to land). So while horizontal landing can't be ruled out, it does indeed seem unlikely to me.

Note also that the Delta Clipper (a vehicle somewhat analogous to what BFS /might/ be) was supposed to land vertically but reentry belly-first, like is shown in the Falcon 9 reuse video. The transition from belly to vertical landing was tested by DC-X in the swan dive test, so it can be done with just engines on the tail (although some thrusters or aerosurfaces/gridfins to assist turning like the booster seems likely):
« Last Edit: 07/11/2016 04:25 PM by Robotbeat »
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Offline Paul451

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Re: MCT Speculation and Discussion Thread 4
« Reply #2385 on: 07/11/2016 04:35 PM »
The image of the "shuttle" in the new article is consistent with the horizontal image from the April article. And Heidmann is tagged as the artist for both. So I doubt he's changed his mind.

From the July article:



Note that there are no engines at the rear, it's more like the Dragon trunk, with doors.

This is consistent with the April article:



And the four belly engines is consistent with the description in the July article.

So clearly when acting as its own second stage, Heidmann is imagining it firing sideways after staging. (Yes, we joked about this earlier in the thread. I even made a little picture. But we were joking.)



Heidmann is also in the "escape module" school. Having the passenger compartment separate upon launch abort. Debated here earlier (and apparently adopted in L2).



...which never made any sense to me. For starters, look how complex that ejection process would have to be, given that most of the escape vehicle is inside the main "shuttle". Are the nose and surround panels ejectable shrouds? Or are they a structural part of the "shuttle", with the escape pod pushing out of a cylindrical slot? If the former, must the shrouds jettison before the LAS engines fire, or (in both cases) are the LAS engines firing inside the "shuttle"? The whole thing is bonkers.

Online envy887

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Re: MCT Speculation and Discussion Thread 4
« Reply #2386 on: 07/11/2016 04:36 PM »
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.

I was really wondering how it goes up, since all the visible engines are pointed to the side during launch.

Offline Paul451

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Re: MCT Speculation and Discussion Thread 4
« Reply #2387 on: 07/11/2016 05:00 PM »
(Also insert my obligatory objection to the completely arbitrary 2RPM limit for AG, necessitating a long tether.

At 5RPM, the two "shuttles" could just dock tail-to-tail and the forward passenger compartment would be at 1g. Moreso, given that Musk's plan is permanent colonisation, he obviously believes that Mars gravity is sufficient for humans permanently. Two "shuttles" docked directly tail-to-tail could provide Mars gravity in the passenger compartment at just 3RPM. And depending on internal mass distribution, a single "shuttle" rotating end-over-end (tumbling pigeon) could provide Mars gravity at 4RPM. No docking and certainly no tether.  Hell, at 7RPM (which recent experiments suggest is tolerable), a 15m "shuttle" can provide Mars gravity by rotating around it's own long axis.

(Of course, in reality, I can't see Musk even looking at AG.))

Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2388 on: 07/11/2016 05:04 PM »
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.
...
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.
« Last Edit: 07/11/2016 05:10 PM by Robotbeat »
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Online envy887

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Re: MCT Speculation and Discussion Thread 4
« Reply #2389 on: 07/11/2016 05:53 PM »
Seems like many of the major architecture points match known MCT plans: TSTO with VTVL booster, all methalox propulsion, LEO refueling, fully reusable booster and orbiter/lander.

While horizontal entry and/or landing seems very backwards to me, I don't know know of any official information that precludes such speculation. There are a lot of speculative biconic designs in this thread.

Offline DanielW

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Re: MCT Speculation and Discussion Thread 4
« Reply #2390 on: 07/11/2016 06:36 PM »
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.

I was really wondering how it goes up, since all the visible engines are pointed to the side during launch.

This is something that I have wondered about. In most phases of the mission a horizontal orientation is better. EDL at both mars and earth, and surface operations. In transit does not care about the orientation. The only part that "wants" to be vertical is the few minutes it takes to leave earth's atmosphere. If you are going to have side mounted engines for super sonic retro propulsion you might as well use them for ascent. 

The trade off is that you move your flip maneuver from just before landing to just after booster separation. That gives you one flip event rather than two. Though I am not sure it is inherently risky enough to matter. I know that as a passenger I would rather perform it once at altitude.

Offline JasonAW3

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Re: MCT Speculation and Discussion Thread 4
« Reply #2391 on: 07/11/2016 06:51 PM »
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.

I was really wondering how it goes up, since all the visible engines are pointed to the side during launch.

This is something that I have wondered about. In most phases of the mission a horizontal orientation is better. EDL at both mars and earth, and surface operations. In transit does not care about the orientation. The only part that "wants" to be vertical is the few minutes it takes to leave earth's atmosphere. If you are going to have side mounted engines for super sonic retro propulsion you might as well use them for ascent. 

The trade off is that you move your flip maneuver from just before landing to just after booster separation. That gives you one flip event rather than two. Though I am not sure it is inherently risky enough to matter. I know that as a passenger I would rather perform it once at altitude.

I'm pretty much of the opinion that the way that he illustrates the side mounted engines for landing simply is too mass heavy to really be accurate.

     I have seen no indications from SpaceX of them even considering development of a vehicle like he describes.

     Overall, I suspect that SpaceX will likely create a large scale version of the Dragon 2 craft as the actual MCT lander.

     Perfecting the landing capability of both the first stage of the F9FT as well as the Dragon 2, would give them practical experience with a similar, but much larger payload structure.  No other type of designs have been even hinted at as yet.

     Development of a completely new design, rather than basing the design on an existing vehicle would be a very expensive and time consuming endeavor that would tend to delay Elon's ambition to get to Mars by at least a half decade, if not longer, and, patient as he is, I doubt very much he'd want to add more delays into the equation than he has to.
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Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2392 on: 07/11/2016 07:01 PM »
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.

I was really wondering how it goes up, since all the visible engines are pointed to the side during launch.

This is something that I have wondered about. In most phases of the mission a horizontal orientation is better. EDL at both mars and earth, and surface operations. In transit does not care about the orientation. The only part that "wants" to be vertical is the few minutes it takes to leave earth's atmosphere. If you are going to have side mounted engines for super sonic retro propulsion you might as well use them for ascent. 
...
Who said you'd have side mounted engines for supersonic retropropulsion?
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Offline DanielW

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Re: MCT Speculation and Discussion Thread 4
« Reply #2393 on: 07/11/2016 07:12 PM »
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.

I was really wondering how it goes up, since all the visible engines are pointed to the side during launch.

This is something that I have wondered about. In most phases of the mission a horizontal orientation is better. EDL at both mars and earth, and surface operations. In transit does not care about the orientation. The only part that "wants" to be vertical is the few minutes it takes to leave earth's atmosphere. If you are going to have side mounted engines for super sonic retro propulsion you might as well use them for ascent. 
...
Who said you'd have side mounted engines for supersonic retropropulsion?

That falls under the speculation part of the threads title. Side entry to maximize drag, and thus to simplify, point the engines that way too. By "simplify" I mean just taking the mars entry / landing piece separately.  If you were only designing a craft that had to land at mars you would make it wide and squat with engines in that direction. Of course you do have to take launch from earth into account but that only means you need to be thin in one plan view. There is no need to put engines on one end. Like you argue with landing, I propose that you can just rotate the craft once out of the atmosphere.

This is not necessarily what I think they will do, but it does not contradict any evidence either and it seems a way to optimize for the hard part of EDL at mars. I admit that it would make structures a bit more complex but if you are going to aeroload from the side anyway you still have to take that mass penalty.

Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2394 on: 07/11/2016 07:20 PM »
It seems very unlikely that SpaceX would launch horizontally from Mars. Nor does horizontal engines on an upper stage make sense.
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Offline pobermanns

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Re: MCT Speculation and Discussion Thread 4
« Reply #2395 on: 07/11/2016 07:22 PM »
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.

I was really wondering how it goes up, since all the visible engines are pointed to the side during launch.

This is something that I have wondered about. In most phases of the mission a horizontal orientation is better. EDL at both mars and earth, and surface operations. In transit does not care about the orientation. The only part that "wants" to be vertical is the few minutes it takes to leave earth's atmosphere. If you are going to have side mounted engines for super sonic retro propulsion you might as well use them for ascent. 
...
Who said you'd have side mounted engines for supersonic retropropulsion?
In that video from Max Fagin, he strongly advocated side-mounted engines to increase the drag. OFC, he was only an intern at SpX, so that doesn't mean that his opinion represents corporate plans.

Offline DanielW

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Re: MCT Speculation and Discussion Thread 4
« Reply #2396 on: 07/11/2016 07:27 PM »
It 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.
« Last Edit: 07/11/2016 07:29 PM by DanielW »

Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2397 on: 07/11/2016 07:30 PM »
It 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).
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Online envy887

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Re: MCT Speculation and Discussion Thread 4
« Reply #2398 on: 07/11/2016 07:34 PM »
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.

I was really wondering how it goes up, since all the visible engines are pointed to the side during launch.

This is something that I have wondered about. In most phases of the mission a horizontal orientation is better. EDL at both mars and earth, and surface operations. In transit does not care about the orientation. The only part that "wants" to be vertical is the few minutes it takes to leave earth's atmosphere. If you are going to have side mounted engines for super sonic retro propulsion you might as well use them for ascent. 
...
Who said you'd have side mounted engines for supersonic retropropulsion?
In that video from Max Fagin, he strongly advocated side-mounted engines to increase the drag. OFC, he was only an intern at SpX, so that doesn't mean that his opinion represents corporate plans.

You will have to define what you mean by side-mounted engines. Dragon's engines are side-mounted but face downward... they cannot be used for a horizontal take-off or horizontal landing. Fagin's proposal is very much like a Dragon in terms of engine setup (he actually used SuperDraco parameters in his simulations).

Side-mounted engines that point perpendicular to the vehicles' long axis are needed for HTHL. The only similar vehicles I can think of are VTVL jets like F-35 and Harrier. Like those jets' ducted exhausts, this think would need to be able to point its rockets backwards at staging... unless it did something weird like go to orbit dorsal side first.

Offline DanielW

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Re: MCT Speculation and Discussion Thread 4
« Reply #2399 on: 07/11/2016 07:38 PM »
It 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).

I will admit to not having specific knowlege there. But I assumed a more lofted trajectory for ease of RTLS as opposed to simply low and slow. The question becomes is the drag significant enough at 100 + km, or wherever they decide to stage, to make it a bad trade. I don't know. But you could fudge your staging higher in the trades if it were an issue. I simply assumed that if you can dump you fairing on a comm sat at that altitude you can probably fly with triple the crossection.

Edit: Also note that the falcon 9 boosters already perform twice the rotation that I am proposing at that altitude so SpaceX does have some experience in that regime.
« Last Edit: 07/11/2016 07:40 PM by DanielW »

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