SpaceX and cis-lunar Space Tourism

[douglas100]

Agree 100%.

I think having another module mounted on the nose of the Dragon makes abort extremely difficult, if not impossible. With this configuration the module would have to be protected by a fairing and would have to separate after the abort to allow the parachutes to deploy safely. Essentially you would have a larger version of Soyuz. It would  be a new spacecraft requiring significant development.

I agree with Chris about docking. This is a mature technology. It has been done hundreds of times. You could even emulate Apollo's conops for transposition and docking. The BEAM module would be mounted on the FH's upper stage and the trunk would act merely as a fairing. The Dragon separates and turns through 180 degrees. The upper stage would provide stability using its own thrusters as the Dragon moves in and docks. Then the stage separates and we're on our way.

[TrevorMonty]

Good points about the aerodynamics of BEAM module attached to Dragon and cold gas thrusters to simplify propulsion.
Assuming Dragon can meet all life support demands of the trip, the BEAM only needs to provide a empty room which will be disposed of at end of the trip.

The issue of not overloading the Dragons max abort weight,  could be solved by having 2 trunks. In an abort the top (lightly loaded) trunk stays with Dragon while lower trunk with bulk of payload eg BEAM, external tanks stays with LV.

 

[douglas100]

Good points about the aerodynamics of BEAM module attached to Dragon and cold gas thrusters to simplify propulsion.
Assuming Dragon can meet all life support demands of the trip, the BEAM only needs to provide a empty room which will be disposed of at end of the trip.

The issue of not overloading the Dragons max abort weight,  could be solved by having 2 trunks. In an abort the top (lightly loaded) trunk stays with Dragon while lower trunk with bulk of payload eg BEAM, external tanks stays with LV.

True, but if you follow the "Apollo solution" BEAM is not in the trunk, but only covered by it. During an abort the Dragon and trunk would separate as "usual" leaving BEAM behind mounted on the upper stage. This solves the overloading during abort problem without needing the extra complexity of two trunks.  However, there might be clearance issues during such an "energetic" separation event.

[Elmar Moelzer]

True, but if you follow the "Apollo solution" BEAM is not in the trunk, but only covered by it. During an abort the Dragon and trunk would separate as "usual" leaving BEAM behind mounted on the upper stage. This solves the overloading during abort problem without needing the extra complexity of two trunks.  However, there might be clearance issues during such an "energetic" separation event.

Do we know for sure that the trunk HAS to stay attached to the capsule during an abort? It seems rather odd to me. I would expect that it could optionally be left behind, unless it is needed to stabilize the capsule somehow.
Also: What about a reusable orbital tug to go between the moon and LEO (launched with a single FH) and then a separate launch (or several F9R launches) for crew and fuel. It would increase the initial cost, but could be cheaper and more flexible in the long term.

[douglas100]

From Elmar Moelzer

Do we know for sure that the trunk HAS to stay attached to the capsule during an abort? It seems rather odd to me. I would expect that it could optionally be left behind, unless it is needed to stabilize the capsule somehow.

I'm assuming that the trunk and its fins are needed for aerodynamic stability during the first part of an abort if it takes place when there is still a substantial atmosphere (Otherwise, what are the fins for? They're not needed as radiators.) If that's not the case, then things are simplified.

Also: What about a reusable orbital tug to go between the moon and LEO (launched with a single FH) and then a separate launch (or several F9R launches) for crew and fuel. It would increase the initial cost, but could be cheaper and more flexible in the long term.

We can come up with more complicated missions involving multiple launches, of course. I was thinking in terms of the simplest possible mission, which I think is the kind most likely to happen first in terms of tourism.

[meekGee]

The fins confuse me.

During the first part of the abort, there's so much input from the SDs that that fins can't passively stabilize the capsule if the SDs are not doing their job.

Maybe after thrust is cut, in the "coast" phase - but then why burn the SDs to depletion?

I actually think that rather than being Fins, they are "pre-deployed, launch-proof" solar cells/radiators - basically they are shaped like fins so that they can survive launch and still give added area on orbit.  They don't really act as stabilizers.

Of course, I admit, why carry the trunk then?  Maybe it helps move the c.m. back, and THAT adds stability - since this property is magnified by the acceleration the SDs provide.

 

[sublimemarsupial]

The fins confuse me.

During the first part of the abort, there's so much input from the SDs that that fins can't passively stabilize the capsule if the SDs are not doing their job.

Maybe after thrust is cut, in the "coast" phase - but then why burn the SDs to depletion?

I actually think that rather than being Fins, they are "pre-deployed, launch-proof" solar cells/radiators - basically they are shaped like fins so that they can survive launch and still give added area on orbit.  They don't really act as stabilizers.

Of course, I admit, why carry the trunk then?  Maybe it helps move the c.m. back, and THAT adds stability - since this property is magnified by the acceleration the SDs provide.

The fins may help stabilize the roll axis, which the SuperDracos do not have very much control authority in (as opposed to the pitch and yaw axes).

[Elmar Moelzer]

The fins confuse me.

Welcome to the club! (we need a beer smiley).

We can come up with more complicated missions involving multiple launches, of course. I was thinking in terms of the simplest possible mission, which I think is the kind most likely to happen first in terms of tourism.

You are right of course. I keep thinking too much about architecture and long term goals. For a short term, simple proof of "we can do it mission", it might be easier to do it all in one launch.
That said, I don't quite understand the need for the Beam module. Just send less people (if all you want is make it work and you don't worry about anything else too much). Dragon is housing 7 people quite comfortably. If you took 4 of those seats out, you would free a lot of room for extra equipment (and a toilet of sorts) and you might be able to increase the operational timeframe a little bit. Might safe some weight as well, especially if you think about the added weight of a Beam.

[Elmar Moelzer]

The fins may help stabilize the roll axis, which the SuperDracos do not have very much control authority in (as opposed to the pitch and yaw axes).

If they are needed for that, how do they control the roll for powered landings?

[douglas100]

We can come up with more complicated missions involving multiple launches, of course. I was thinking in terms of the simplest possible mission, which I think is the kind most likely to happen first in terms of tourism.

You are right of course. I keep thinking too much about architecture and long term goals. For a short term, simple proof of "we can do it mission", it might be easier to do it all in one launch.
That said, I don't quite understand the need for the Beam module...

I think you're right, it probably isn't necessary for a "minimalist" mission. But if one were to be carried, then I think the "Apollo solution" is a straightforward way of doing it.

[Burninate]

The fins confuse me.

Welcome to the club! (we need a beer smiley).

We can come up with more complicated missions involving multiple launches, of course. I was thinking in terms of the simplest possible mission, which I think is the kind most likely to happen first in terms of tourism.

You are right of course. I keep thinking too much about architecture and long term goals. For a short term, simple proof of "we can do it mission", it might be easier to do it all in one launch.
That said, I don't quite understand the need for the Beam module. Just send less people (if all you want is make it work and you don't worry about anything else too much). Dragon is housing 7 people quite comfortably. If you took 4 of those seats out, you would free a lot of room for extra equipment (and a toilet of sorts) and you might be able to increase the operational timeframe a little bit. Might safe some weight as well, especially if you think about the added weight of a Beam.

Dragon is housing 7 heavily screened volunteer NASA astronauts wearing space suits and diapers, planning on being in that situation for at most about 2 days, but more likely about six hours.  There's only 10m^3 of air ("pressurized volume") in the whole vehicle, before considering cargo or increased life support needs.  A Lunar free return trajectory is a ~6 day maneuver.  The average *coffin* has about 0.9m^3 of airspace - that's less than 2 coffins per person.

For comparison: the Shuttle, which flew comparable crews, had 74.3m^3 of pressurized volume, and the Soyuz flies 3 people in 7.5m^3 (2.5m^3 in the landing module, which essentially everybody remarks is claustrophobic/uncomfortable, but which they're only confined to for hours at a time).

Tourists are going to want more.  Treat the Dragon as a place to launch from and reenter the atmosphere, and no more, for that purpose - even with a diminished crew of 4 it's as cramped as Soyuz.

[douglas100]

The fins confuse me.

During the first part of the abort, there's so much input from the SDs that that fins can't passively stabilize the capsule if the SDs are not doing their job.

If the abort takes place from the pad or at low altitude, that may be true. But at high speed--maxQ for example, the capsule itself would not not aerodynamically stable nose forward. Its centre of mass is so positioned that it would tend to tumble to blunt end forward when released into the air stream.  You don't want that if you're trying to get away from a speeding LV. Now if the Dracos and SD's are powerful and can react fast enough to overcome these aerodynamic forces, no problem. However, my take is that SpaceX have modeled this and have almost certainly done wind tunnel tests and have decided that aerodynamic stabilization is required.

I actually think that rather than being Fins, they are "pre-deployed, launch-proof" solar cells/radiators - basically they are shaped like fins so that they can survive launch and still give added area on orbit.  They don't really act as stabilizers.

If they don't act as stabilizers they don't need four. Only two carry solar cells. If that was their only purpose two could be omitted. I don't buy the radiator argument. There is a large area on the antisolar side of the trunk for radiators.

Let's not overthink this. I suggest that the fins are exactly what they appear to be: aerodynamic stabilizers.

[Elmar Moelzer]

Dragon is housing 7 heavily screened volunteer NASA astronauts wearing space suits and diapers, planning on being in that situation for at most about 2 days, but more likely about six hours. 

That's why I suggested to do a lunar mission with only 3 people on board, instead of 7.

There's only 10m^3 of air ("pressurized volume") in the whole vehicle, before considering cargo or increased life support needs.  A Lunar free return trajectory is a ~6 day maneuver.  The average *coffin* has about 0.9m^3 of airspace - that's less than 2 coffins per person.

Again, I was talking 3 people, not 7. That would more than double the room per person.
Also Dragon was said to be able to remain autonomous for up 10 days. So with reduced crew and additional supplies it might be doable. Sure it would not be comfortable, but I was told that this was meant as an example for a "minimum mission" kind of thing.

Tourists are going to want more.

Hence my suggestion of a separately launched orbital tug, which could have significantly more living space (and would be reusable and probably cheaper in the long term). But for a "minimal mission", I think just the Dragon should be fine.

[ChrisWilson68]

What about a reusable orbital tug to go between the moon and LEO (launched with a single FH) and then a separate launch (or several F9R launches) for crew and fuel. It would increase the initial cost, but could be cheaper and more flexible in the long term.

Yes, I agree that's the way to go in the long term.  There should be specialized reusable vehicles (such as Dragon V2, but others could also fill the role) that only transport people between the Earth's surface and LEO.  At LEO, people should transfer to vehicles that stay in space and are resused, no matter where they're going or staying.

I hope we get to that long-term way of thinking sooner rather than later.  Falcon 9/Falcon Heavy/Dragon represents that way of thinking -- make the Earth-to-orbit-and-back system reusable and do many flights.  Falcon 9 and Falcon Heavy are perfect for bringing up lots of propellant and supplies on many flights.  SLS is the opposite approach, where nothing is reusable, flight rates are low, and we have no leverage to scale anything.

Having a habitat launched with a Dragon is a step in the wrong direction, in my opinion -- a step toward the throw-it-away mindset.

[Space Ghost 1962]

The fins confuse me.

During the first part of the abort, there's so much input from the SDs that that fins can't passively stabilize the capsule if the SDs are not doing their job.

If the abort takes place from the pad or at low altitude, that may be true. But at high speed--maxQ for example, the capsule itself would not not aerodynamically stable nose forward. Its centre of mass is so positioned that it would tend to tumble to blunt end forward when released into the air stream.  You don't want that if you're trying to get away from a speeding LV.

No. On max-Q abort, the stability comes from nailing the capsule to the shock wave ahead of the capsule, and the software can adjust the throttle's of each engine to not only stabilize the craft but moderate turbulence of flow / flow separation issues.

Now if the Dracos and SD's are powerful and can react fast enough to overcome these aerodynamic forces, no problem. However, my take is that SpaceX have modeled this and have almost certainly done wind tunnel tests and have decided that aerodynamic stabilization is required.

I actually think that rather than being Fins, they are "pre-deployed, launch-proof" solar cells/radiators - basically they are shaped like fins so that they can survive launch and still give added area on orbit.  They don't really act as stabilizers.

If they don't act as stabilizers they don't need four. Only two carry solar cells. If that was their only purpose two could be omitted. I don't buy the radiator argument. There is a large area on the antisolar side of the trunk for radiators.

Let's not overthink this. I suggest that the fins are exactly what they appear to be: aerodynamic stabilizers.

Yes they need four - because if there were two, the absence of the others would amplify buffeting/turbulence on ascent.

The fins increase surface area. Defacto radiators no matter what.

My take on why they are there - the asymmetrical X pattern of thruster housings in the vertical airstream amplify (as above) on ascent. It throws off the precision of the guidance system and creates feedback terms for the software that aren't easy to cope with. Easier to buy back stability passively. E.g. a "quick fix"

Perhaps long term they change the mold line and the fins vanish, More payload to orbit. Don't sweat it.

[ChrisWilson68]

The fins confuse me.

During the first part of the abort, there's so much input from the SDs that that fins can't passively stabilize the capsule if the SDs are not doing their job.

If the abort takes place from the pad or at low altitude, that may be true. But at high speed--maxQ for example, the capsule itself would not not aerodynamically stable nose forward. Its centre of mass is so positioned that it would tend to tumble to blunt end forward when released into the air stream.  You don't want that if you're trying to get away from a speeding LV.

No. On max-Q abort, the stability comes from nailing the capsule to the shock wave ahead of the capsule, and the software can adjust the throttle's of each engine to not only stabilize the craft but moderate turbulence of flow / flow separation issues.

I don't buy that.  I think the fins buy you passive stability in an abort.  The software can just open the throttle up all the way on all engines on abort and it will be stable.  There's less that can go wrong with that approach than with an active-stability approach where the computer has to do fine throttle adjustments.

There's no plausible reason for the trunk to stay attached in an abort other than for stability.  If the trunk is there for stability, it's not much of a stretch to see that the fins might be too.

Edit: But on further reflection, this probably isn't the ideal thread for debating the reasons for fins.  Perhaps we can take further discussion to a more appropriate thread?

[Space Ghost 1962]

No. On max-Q abort, the stability comes from nailing the capsule to the shock wave ahead of the capsule, and the software can adjust the throttle's of each engine to not only stabilize the craft but moderate turbulence of flow / flow separation issues.

I don't buy that.  I think the fins buy you passive stability in an abort.  The software can just open the throttle up all the way on all engines on abort and it will be stable.  There's less that can go wrong with that approach than with an active-stability approach where the computer has to do fine throttle adjustments.

There's no plausible reason for the trunk to stay attached in an abort other than for stability.  If the trunk is there for stability, it's not much of a stretch to see that the fins might be too.

On abort the fins are BEHIND you on a SEPARATE VEHICLE. Not coupled.

Furthermore, you have a HUGE stagnation that will occur once the Dragon sans trunk exposes the trunk to the high Mach shockwave. Will be like hitting a brick wall.

During separation, thrust smacks Dragon against a max-Q wall and the bending deviations below dragon are inconsequential until stream separation - nothing can outrun the incident shock wave, which acts as a barrier as the trunk breaks up.

There is nothing in the plane of separation that interferes with Dragon at the separation instant and beyond.

So how does it matter, how does it help?

[sublimemarsupial]

On abort the fins are BEHIND you on a SEPARATE VEHICLE. Not coupled.

As per the pad abort test plan, the trunk (and its fins) stays attached to Dragon during the abort, and is only separated after a safe distance from the vehicle is achieved and the drogue parachutes are deployed.

[douglas100]

...Edit: But on further reflection, this probably isn't the ideal thread for debating the reasons for fins.  Perhaps we can take further discussion to a more appropriate thread?

Since I brought up the question of the fins I'm partly responsible for take this off course. Agree.

[TrevorMonty]

Here is my costing estimates for lunar flyby.
$135m. ELV FH
$10m. Use of reusable Dragon
$20m. Expendable BEAM
$45m. Profit and extras

Say $210m. If mission can handle 4 ie 1 pilot + 3 passengers. That is $70m each. NB with 4 one row of seats can be removed, freeing up a lot of space.

If boosters are recoverable we maybe able to save $60m making it $50M a seat.

At these prices there maybe a market for one or two flights a year.