Author Topic: Dragon 2 or Starliner derived dedicated lunar lander?  (Read 66224 times)

Offline Space Ghost 1962

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Re: Dragon 2 or Starliner derived dedicated lunar lander?
« Reply #120 on: 03/07/2017 06:53 pm »
Keep in mind the side mount and need to launch under an existing fairing. Also, you need to have vertical mount not canted for aeroshell conformance.

Offline Negan

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Re: Dragon 2 or Starliner derived dedicated lunar lander?
« Reply #121 on: 03/07/2017 07:11 pm »
If you are running sets of engines on both sides anyway why not launch the lander on its side and make it more rectangular? The cabin (or capsule) is in the middle and everything is disbursed to the sides including the equipment that would normally be under it that is part of the trunk. Hatch would be closer to the ground also. You would have do something creative to take the some of the load off of the side of the lander during launch.

Edit: Maybe even use two trunks for the side structures on each side.
« Last Edit: 03/07/2017 07:48 pm by Negan »

Online envy887

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Re: Dragon 2 or Starliner derived dedicated lunar lander?
« Reply #122 on: 03/07/2017 07:54 pm »
About 340-345 seconds with a highly expanded nozzle extension. This is consistent with other pump-fed NTO-MMH vacuum engines that operate at similar chamber pressures (e.g. Aestus II).

The SuperDraco is designed for short duration burns, but it is regeneratively cooled and designed for reuse so longer duration burns are probably feasible. The nozzle extension would probably need to be radiatively cooled.

What nozzle diameter would be required?  I'd like to put a rendering together for discussion purposes based off the known pressure vessel dimensions.

Also, what happens to the ISP if the SD's are ran at a lower throttle setting to allow for adequate expansion with smaller nozzles?  At 71kN max thrust per engine even 4 SD's would be more than enough rather than 8.

I get 110 kN and 343 seconds at 6.9 MPa and 140:1 expansion. The SuperDraco throat appears to be 0.100 m in diameter, so 140:1 expansion requires a 1.20 m diameter nozzle (which would be 1.68 m long for a 90% bell or 1.21 m long for a 65% bell that still gets 340 second ISP).

Vacuum ISP is mostly independent of chamber pressure (throttle): reducing pressure to 70% reduces ISP from 343 seconds only to 342 seconds, and going all the way to 20% throttle only reduces ISP to 336 seconds.

You can almost infinitely vary nozzle diameter and length to fit in various packages with different performance levels. Try downloading RPA lite and plugging some of these values in to see where the optimal nozzle is for your size requirements.

Offline Space Ghost 1962

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Re: Dragon 2 or Starliner derived dedicated lunar lander?
« Reply #123 on: 03/07/2017 08:44 pm »
If you are running sets of engines on both sides anyway why not launch the lander on its side and make it more rectangular? The cabin (or capsule) is in the middle and everything is disbursed to the sides including the equipment that would normally be under it that is part of the trunk. Hatch would be closer to the ground also. You would have do something creative to take the some of the load off of the side of the lander during launch.

Edit: Maybe even use two trunks for the side structures on each side.

Use an sheet metal cylinder sidewall similar to F9 stage tank construction with no cant. Use the additional volume to allow more lower tankage w/o affecting crew volume. Isolate lines externally with MLI.

Offline Negan

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Re: Dragon 2 or Starliner derived dedicated lunar lander?
« Reply #124 on: 03/07/2017 08:51 pm »
Bonus it will look like a TIE fighter.  ;D

Offline lamontagne

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Re: Dragon 2 or Starliner derived dedicated lunar lander?
« Reply #125 on: 03/07/2017 11:50 pm »
53 tonnes maxed out tanker and lander.

Just barely does all the required performances.  But it makes for an awfully tall stack on the moon.
I guess we could launch the whole thing inside a fairing as well, with the crew launches separately in a falcon 9?

« Last Edit: 03/07/2017 11:52 pm by lamontagne »

Online envy887

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Re: Dragon 2 or Starliner derived dedicated lunar lander?
« Reply #126 on: 03/08/2017 12:24 am »
53 tonnes maxed out tanker and lander.

Just barely does all the required performances.  But it makes for an awfully tall stack on the moon.
I guess we could launch the whole thing inside a fairing as well, with the crew launches separately in a falcon 9?

SuperDraco is pressure-fed. Will those tanks hold 1000+ psi?

Offline MATTBLAK

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Re: Dragon 2 or Starliner derived dedicated lunar lander?
« Reply #127 on: 03/08/2017 12:43 am »
53 tonnes maxed out tanker and lander.

Just barely does all the required performances.  But it makes for an awfully tall stack on the moon.
I guess we could launch the whole thing inside a fairing as well, with the crew launches separately in a falcon 9?


Yes - which is why a Crasher Stage has been mentioned a couple times, in part so as to not make the Lander too tall.
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Offline GWH

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Re: Dragon 2 or Starliner derived dedicated lunar lander?
« Reply #128 on: 03/08/2017 01:17 am »
53 tonnes maxed out tanker and lander.

Just barely does all the required performances.  But it makes for an awfully tall stack on the moon.
I guess we could launch the whole thing inside a fairing as well, with the crew launches separately in a falcon 9?

Small note: you have 3 engines shown in all the TWR calcs.
What material did you assume for the tanks? SuperDraco mass?

Offline lamontagne

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Re: Dragon 2 or Starliner derived dedicated lunar lander?
« Reply #129 on: 03/08/2017 01:19 am »
53 tonnes maxed out tanker and lander.

Just barely does all the required performances.  But it makes for an awfully tall stack on the moon.
I guess we could launch the whole thing inside a fairing as well, with the crew launches separately in a falcon 9?

SuperDraco is pressure-fed. Will those tanks hold 1000+ psi?
No.  They are much too large.  A 3m diameter COPV tank might just survive 1000 PSI.  But without much safety margin, even with a 1 cm wall.  The 5m dia. tank explodes.
Back to the drawing board :-)

Perhaps a turbine fed equivalent for the engine? 


Offline lamontagne

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Re: Dragon 2 or Starliner derived dedicated lunar lander?
« Reply #130 on: 03/08/2017 01:24 am »
53 tonnes maxed out tanker and lander.

Just barely does all the required performances.  But it makes for an awfully tall stack on the moon.
I guess we could launch the whole thing inside a fairing as well, with the crew launches separately in a falcon 9?

Small note: you have 3 engines shown in all the TWR calcs.
What material did you assume for the tanks? SuperDraco mass?
COPV, but that fails for large tanks.  Need a less drastic engine.
I also had 10T rather than 7, but that's not too bad.  I think i'll illustrate three engines.  4 seems overpowered.

Offline lamontagne

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Re: Dragon 2 or Starliner derived dedicated lunar lander?
« Reply #131 on: 03/08/2017 01:26 am »
53 tonnes maxed out tanker and lander.

Just barely does all the required performances.  But it makes for an awfully tall stack on the moon.
I guess we could launch the whole thing inside a fairing as well, with the crew launches separately in a falcon 9?


Yes - which is why a Crasher Stage has been mentioned a couple times, in part so as to not make the Lander too tall.

Could we soft land the crasher stage?  Might be useful.
How bad is a tall lander? 

Offline lamontagne

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Re: Dragon 2 or Starliner derived dedicated lunar lander?
« Reply #132 on: 03/08/2017 01:32 am »
Both vehicles under a fairing.

I guess the lander could separate in two just before landing, and land on the superdracos.  We would need some extra fuel for lift off though.  Perhaps we need three elements for the lander?  I'll try another image.
« Last Edit: 03/08/2017 02:23 am by lamontagne »

Online envy887

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Re: Dragon 2 or Starliner derived dedicated lunar lander?
« Reply #133 on: 03/08/2017 01:38 am »
Why are you launching 51 tonnes of hypergols? The Falcon upper stage is more efficient for TLI, and you don't need that much fuel after TLI.

Offline Space Ghost 1962

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Re: Dragon 2 or Starliner derived dedicated lunar lander?
« Reply #134 on: 03/08/2017 01:43 am »
53 tonnes maxed out tanker and lander.

Just barely does all the required performances.  But it makes for an awfully tall stack on the moon.
I guess we could launch the whole thing inside a fairing as well, with the crew launches separately in a falcon 9?

SuperDraco is pressure-fed. Will those tanks hold 1000+ psi?
Unlikely. And, if they did, likely too heavy.

Such an approach argues for pump fed engines. Possibly electrically run (see upthread suggestion) off of high density Li-ion rechargables, as your burn times will be short, you've got excess array power, and sufficient recharge time between burns. So even better than Electron.

Offline lamontagne

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Re: Dragon 2 or Starliner derived dedicated lunar lander?
« Reply #135 on: 03/08/2017 01:54 am »
Here is a version with a crasher stage.  LAnder with and without fairing.


Offline GWH

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Re: Dragon 2 or Starliner derived dedicated lunar lander?
« Reply #136 on: 03/08/2017 01:56 am »
Perhaps a turbine fed equivalent for the engine?

I suggested up thread using electric turbopumps.  I used the Electron to give me a rough idea on mass:
1st stage 9250 kg prop, 355 sec burntime
(9) pumps at 37 kw power delivered, 355 sec  = 33kwh*0.9 motor eff.*0.9 pump eff. = 41kwh storage required
Battery mass @ 0.265 kwh/kg = 153 kg.  Round up to 170 kg for some margin.  Lunar Dragon may need less than this, depends on the total amount of prop required for descent phase.

Now if the Dragon doesn't need any of the existing pressurized prop tanks and helium how much could it save?

I have been playing around with some numbers and shedding some weight have the total dry mass of everything at 5600kg (could be low), prop load at LLO required 15000kg, and using a 2.1m dia x 4.3m tank in place of the trunk so that the 4xsuperdraco vac engines can be tucked up under the pressure vessel, and not canted.  This would require stripping out the existing propellant tanks that are stuffed under the widest part of the PV. The tanks could of course be laid out like a proton in between the SD's to save some height, but this would be less mass.
 It's just a sketch at the moment so go easy on me...
« Last Edit: 03/08/2017 02:19 am by GWH »

Offline Negan

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Re: Dragon 2 or Starliner derived dedicated lunar lander?
« Reply #137 on: 03/08/2017 02:06 am »
If you are running sets of engines on both sides anyway why not launch the lander on its side and make it more rectangular? The cabin (or capsule) is in the middle and everything is disbursed to the sides including the equipment that would normally be under it that is part of the trunk. Hatch would be closer to the ground also. You would have do something creative to take the some of the load off of the side of the lander during launch.

Edit: Maybe even use two trunks for the side structures on each side.

Use an sheet metal cylinder sidewall similar to F9 stage tank construction with no cant. Use the additional volume to allow more lower tankage w/o affecting crew volume. Isolate lines externally with MLI.

As a side note if you didn't have a capsule in the middle, you could put a flat platform instead and use it as a cargo only hauler. The ramp to unload would be minimal since you're still close to the ground.

Edit: Or skip the platform and use the skycrane technique.
« Last Edit: 03/08/2017 03:48 am by Negan »

Offline lamontagne

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Re: Dragon 2 or Starliner derived dedicated lunar lander?
« Reply #138 on: 03/08/2017 02:06 am »
Why are you launching 51 tonnes of hypergols? The Falcon upper stage is more efficient for TLI, and you don't need that much fuel after TLI.

I'm just using the 54 tonnes SpaceX spec to LEO as my baseline.  The super draco with a vacuum nozzle seemed to give almost the same performance as the second stage Merlin, 345 ISP vs 348, might provide less boil off problems and would be a dedicated long range design, rather than a significant change to the  Falcon upper stage.  Unfortunately my propellant tank exploded under high pressure  :-(
So I'm looking for a new engine, or a turbo pump super draco design.

For the Falcon heavy payloads to beyond LEO, 13 T to Mars for example, is it the second stage operating for a longer time, or is a dedicated third stage required, rather like a telecommunication satellite?


Offline Rocket Science

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Re: Dragon 2 or Starliner derived dedicated lunar lander?
« Reply #139 on: 03/08/2017 03:13 pm »
 Here is my latest Reusable Dragon Horizontal lander simple carbon fiber truss frame with RP1/LOX drop tank (orange), grey section is a payload drop-pallet, engine MVac. Retractable solar array deployed on upper surface (dark blue), fold-out ladder to surface inside bottom hatch. Basically a Falcon S2 rear section to perform deorbit burn to lunar surface with Super Dracos performing the flare to land. Leave drop-tank tank on surface during lift-off with 8 Super Dracos, MVac engine stays attached to rear truss. O2 tanks light blue, He tanks green, hypergolic prop purple.

 If you wanted to do suit-ports, they could be on an inner bulkhead and stored there and protected by the outer hatch cover. Open back suit-port cover, climb in, open the outer hatch and unfold the ladder and descend the few steps to the surface...
« Last Edit: 03/13/2017 11:06 pm by Rocket Science »
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