Hypothetical new Falcon 1 type LV

[fwskungen]

yeh i suppose you will lose ISP the question tho is how much ISP one will lose i find the kestrel engine to have a ISP of 317   the only ISP i can find for the superdracos is 240 this is most likely sea level and with no bell. So anybody want to guess.

[Lars-J]

For a Falcon9/Falcon Heavy Payload Assist Module, the idea of using superdraco for the application might have some merit for deep space missions like interplanetary probes, or insertions to GEO. I think though that SpaceX have decided to maximize the Falcon architecture recoverable/re-usable fraction, so a development program like that might be viewed by them as counter-intuitive.

For an imaginary F1e, I think that the superdracos' low Isp would help less than a better Kestrel2.

No, it has little merit for a deep space mission. Once you are out of the deep gravity well, Isp is king. Thrust does not matter. So a Draco (or cluster of them) would actually be superior to SuperDraco for the purpose of a final kick stage.

[abaddon]

No, it has little merit for a deep space mission. Once you are out of the deep gravity well, Isp is king. Thrust does not matter. So a Draco (or cluster of them) would actually be superior to SuperDraco for the purpose of a final kick stage.

Not that I disagree with you, but a Star 48 has an ISP of 292 (see http://forum.nasaspaceflight.com/index.php?topic=33084.msg1109220#msg1109220) which is also really poor.  SpaceX built the SuperDraco to essentially compete with an SRM: low ISP, high thrust, quick ignition, non-cryo propellant, with the notable difference being that it can throttle dynamically instead of being stuck with a fixed thrust profile.

But if you're going to do all of that, in space, a SRM has much better storability properties, probably weighs less (when you account for the plumbing), and is a known and available quantity already.  Just use a Star 48 or equivalent if that's what you want!

Really, SuperDracos were designed for a very specific purpose, and trying to use them elsewhere just doesn't make sense at all.

[Stan-1967]

Well now, this is my kind of thread.

Well I took the leap last night to give my best effort at making my own new "Phoenix" F1 class vehicle and testing it out on a simulator linked to by this site in the archives at Silverbird Astronautics.
http://www.silverbirdastronautics.com/LVperform.html
[...]
Here is what the calculations returned:
Mission Performance:
Launch Vehicle:     User-Defined Launch Vehicle
Launch Site:     Cape Canaveral / KSC
Destination Orbit:     185 x 185 km, 45 deg
Estimated Payload:     1687 kg
95% Confidence Interval:     1294 - 2172 kg
[...]

So... assuming I was a billionaire, I had a couple of Mercury style capsules as payloads (m = 1400kg), and a death defying love of Koalas, I could have lunch in Cape Canaveral, get on a Phoenix at 3pm, have breakfast in Taronga zoo, Sydney (at 4pm/8am), get on another Phoenix at 5pm/9am and be back at KSC in time for dinner?

That was my thoughts after posting the numbers as well!   "Hey...that enough mass for a Mercury capsule!"   However in addition for your love of Koalas, you must also be a billionaire who aspires to be a millionaire.
 

[Stan-1967]

No, it has little merit for a deep space mission. Once you are out of the deep gravity well, Isp is king. Thrust does not matter. So a Draco (or cluster of them) would actually be superior to SuperDraco for the purpose of a final kick stage.

But if you're going to do all of that, in space, a SRM has much better storability properties, probably weighs less (when you account for the plumbing), and is a known and available quantity already.  Just use a Star 48 or equivalent if that's what you want!

Really, SuperDracos were designed for a very specific purpose, and trying to use them elsewhere just doesn't make sense at all.

The Star 48 also has some excellent mass ratios that make it attractive in spite of the low ISP.

When I ran my sims for my Falcon 1 class vehicle, I did a lot of runs with various upper stage configurations, but my lessons agreed with what you would expect.

Every kg of propellant expended in a low ISP upper stage is a 1:1 mass penalty to payload.  ISP matters a lot!

Total thrust to weight also matters in getting S2 from MECO to LEO.   I modeled a 50kN, 100kN, and 150kN upper stage ( same ISP)  with the associated mass trades, and taking burning a smaller 50kN engine longer, with more gravity losses, dropped payload  several hundred kg's.   Alternately, using a heavier 150kN engine and having less available propellant also dropped the payload in comparison to the 100kN engine.

If I had to say how I'd prioritize my S2 engine, It would come down to the destination.  ( LEO or GEO etc. ) the higher the orbit, the ISP will rule.   Getting from S2 ignition to LEO was also sensitive to T/W and minimizing burn time without too heavy of an engine.

final edit:  This is exactly what you see play out with the F9 vehicle and the Merlin 1D-Vac upper stage.  A great T/W engine that quickly burns it's way to LEO.  Payload to LEO is fantastic, but drops off rapidly to higher orbits in comparison to other vehicles using high ISP upper stages.   Every kg of inneficient 340 ISP exhaust from the 1D-Vac eats into payload that gets to a higher orbit.

[MP99]

I suspect that the best way for SpaceX to tackle this market would be to put the development funds into making the F9 upper stage reusable instead.

This would be a big performance hit to F9, but should cover the market that F1 would otherwise cover.

Cheers, Martin

[CuddlyRocket]

Remembering that this is supposed to be a low-cost launcher and its design should therefore be optimised for cost, not performance, I'd suggest the following design parameters: Common propellant for both stages and using existing equipment where possible.

Given the above, how about the following proposal: A 2-stage rocket; both stages keralox with a single M1-D SL engine? The SL version is not as efficient as the Vac in space, but it should be sufficient (it has a vacuum isp of 308 versus 348). It's also lower thrust, which helps with problems of over-acceleration on the second stage (and it can throttle down to 70%).

Anyone care to run the numbers?

[S.Paulissen]

Remembering that this is supposed to be a low-cost launcher and its design should therefore be optimised for cost, not performance, I'd suggest the following design parameters: Common propellant for both stages and using existing equipment where possible.

Given the above, how about the following proposal: A 2-stage rocket; both stages keralox with a single M1-D SL engine? The SL version is not as efficient as the Vac in space, but it should be sufficient (it has a vacuum isp of 308 versus 348). It's also lower thrust, which helps with problems of over-acceleration on the second stage (and it can throttle down to 70%).

Anyone care to run the numbers?

Won't work, too much thrust for a merlin on second stage at minimum throttle the upper stage would hit 20gs at burn out.

[Lars-J]

Remembering that this is supposed to be a low-cost launcher and its design should therefore be optimised for cost, not performance, I'd suggest the following design parameters: Common propellant for both stages and using existing equipment where possible.

Given the above, how about the following proposal: A 2-stage rocket; both stages keralox with a single M1-D SL engine? The SL version is not as efficient as the Vac in space, but it should be sufficient (it has a vacuum isp of 308 versus 348). It's also lower thrust, which helps with problems of over-acceleration on the second stage (and it can throttle down to 70%).

Anyone care to run the numbers?

Won't work, too much thrust for a merlin on second stage at minimum throttle the upper stage would hit 20gs at burn out.

Not if the 2nd stage is actually larger than the 1st stage.

[Dante80]

That would be somewhat counter-productive I think. A single m1-d can move..eh...lets say about 70,000kg off the pad for a low TWR. Lets say that S2 is bigger (40 tonnes, including payload). This means that the first stage should weigh about 30 tonnes.

M1-d does about 84,000kgf in vacuum (we are still talking about the SL version, not MVac). How much could you feasibly throttle it down before the payload liquefies?

[Patchouli]

No, it has little merit for a deep space mission. Once you are out of the deep gravity well, Isp is king. Thrust does not matter. So a Draco (or cluster of them) would actually be superior to SuperDraco for the purpose of a final kick stage.

Not that I disagree with you, but a Star 48 has an ISP of 292 (see http://forum.nasaspaceflight.com/index.php?topic=33084.msg1109220#msg1109220) which is also really poor.  SpaceX built the SuperDraco to essentially compete with an SRM: low ISP, high thrust, quick ignition, non-cryo propellant, with the notable difference being that it can throttle dynamically instead of being stuck with a fixed thrust profile.

But if you're going to do all of that, in space, a SRM has much better storability properties, probably weighs less (when you account for the plumbing), and is a known and available quantity already.  Just use a Star 48 or equivalent if that's what you want!

Really, SuperDracos were designed for a very specific purpose, and trying to use them elsewhere just doesn't make sense at all.

Another option use a hypergolic upper stage engine such as the AJ-10 or Aestus.

[Lars-J]

That would be somewhat counter-productive I think. A single m1-d can move..eh...lets say about 70,000kg off the pad for a low TWR. Lets say that S2 is bigger (40 tonnes, including payload). This means that the first stage should weigh about 30 tonnes.

M1-d does about 84,000kgf in vacuum (we are still talking about the SL version, not MVac). How much could you feasibly throttle it down before the payload liquefies?

My point is that is your upper stage is large enough, the situation is no different than what current small F9 payloads experience - such as CASSIOPE, DISCOVR, and now JASON-3 - and somehow those payloads don't seem to "liquefy". You are exaggerating the issue of g-loads at burnout.

[Dante80]

My pony is that is your upper stage is large enough, the situation is no different than what current small F9 payloads experience - such as CASSIOPE, DISCOVR, and now JASON-3 - and somehow those payloads don't seem to "liquefy". You are exaggerating the issue of g-loads at burnout.

I think that its not the same thing man. Running the numbers for a 110+ ton S2 lifted by 9 M-1ds to a 40 ton S2 lifted by one makes me think that the situation is different at S2 burnout with a small payload.

[hkultala]

Well I took the leap last night to give my best effort at making my own new "Phoenix" F1 class vehicle and testing it out on a simulator linked to by this site in the archives at Silverbird Astronautics.
http://www.silverbirdastronautics.com/LVperform.html

This was the first time I have ever done an exercise like this.  I have watched many other here do similar, some of you are very very good at it.  I do not profess to be good at all.

My designs started with the specifications for using the Merlin 1D FT engine w/ 756 kN thrust, and building the vehicle around that.  I also made an early decision to make the new vehicle with a 2m core, not the 1.7 I believe the old F1 had.  I think the Merlin 1D FT is too much rocket to stick on that small a diameter core without getting something too long and bendy.

I also wanted to make a better S2, so I selected to use a 100kN Methane upper stage.  ( Darma Technolgies CHASE 10 ) I had to guess what a vacuum engine could do for ISP, and guessed 350s.

G's at liftoff were set to be 1.18, so the mass of the complete vehicle would then be 65329 kg's.

After some iterations on the calculations, my mass distribution is a follows

Stage 1:
Dry mass = 3461 kg
Propellant = 55368 kg
Thrust = 756 kN
ISP avg = 304

Stage 2:
Dry mass = 619
Propellant = 5881
Trust = 100 kN
ISP = 350
Fairing 160 kg

Second stage having better T/W than first stage does not look like a very balanced design.

If your engine specs are fixed, consider moving some propellant from the first stage to the second stage.

[S.Paulissen]

That would be somewhat counter-productive I think. A single m1-d can move..eh...lets say about 70,000kg off the pad for a low TWR. Lets say that S2 is bigger (40 tonnes, including payload). This means that the first stage should weigh about 30 tonnes.

M1-d does about 84,000kgf in vacuum (we are still talking about the SL version, not MVac). How much could you feasibly throttle it down before the payload liquefies?

My pony is that is your upper stage is large enough, the situation is no different than what current small F9 payloads experience - such as CASSIOPE, DISCOVR, and now JASON-3 - and somehow those payloads don't seem to "liquefy". You are exaggerating the issue of g-loads at burnout.

This is a false equivalence for a couple of reasons.

A) The dry weight of the second stage in small payload cases like JASON-3 is that the second stage comes with its own ballast mass, excess propellant.  The second stage in a case like JASON-3 is at roughly target orbital speed with 13000kg of propellant still in the tanks leaving a small payload like this with only 3g acceleration at burn out.  This rockets full performance is required, burning all the way to empty, so there is no built in ballast, thus achieving very high gs.

B) Transferring that much propellant to the upper stage would cost considerable performance as it's mainly the loss of dry mass at staging that increases performance.  How much are you proposing to transfer in order to achieve normal launch g forces?

[Stan-1967]

Remembering that this is supposed to be a low-cost launcher and its design should therefore be optimised for cost, not performance, I'd suggest the following design parameters: Common propellant for both stages and using existing equipment where possible.

Given the above, how about the following proposal: A 2-stage rocket; both stages keralox with a single M1-D SL engine? The SL version is not as efficient as the Vac in space, but it should be sufficient (it has a vacuum isp of 308 versus 348). It's also lower thrust, which helps with problems of over-acceleration on the second stage (and it can throttle down to 70%).

Anyone care to run the numbers?

I just ran a sim on a S1 and S2 with equal mass ( 3300 kg dry weight, 31600kg propellant ).

Results were not impressive:( but that what 2 stages with crappy mass ratios will get you )
=====================
Mission Performance:
Launch Vehicle:     User-Defined Launch Vehicle
Launch Site:     Cape Canaveral / KSC
Destination Orbit:     185 x 185 km, 45 deg
Estimated Payload:     0 kg
95% Confidence Interval:     0 - 0 kg
======================

It is pushing 21 g's at burnout.

I appreciate the goal of using the same fuel for both stages to make this exercise about a low cost/simple rocket.  I did consider a cluster of "Rutherford" class electric pump fed engines.   Rocketlab hasn't published much regarding ISP for a vacuum Rutherford.  I recall seeing ISP of 327s speculated somewhere around here.  I  ran a sim with 4 Rutherford vac engines producing 100kN and aloted an additional 100 kg of battery  mass to the empty mass in the sim I did with the CHASE 10 Methalox.  ( no idea what real numbers would be for the battery) Here is how that played out:
=======================
Mission Performance:
Launch Vehicle:     User-Defined Launch Vehicle
Launch Site:     Cape Canaveral / KSC
Destination Orbit:     185 x 185 km, 45 deg
Estimated Payload:     1368 kg
95% Confidence Interval:     994 - 1830 kg
=======================

Not too bad performance, and if you can 3-D print your engine, low cost should be attainable.

[Lars-J]

My point is that is your upper stage is large enough, the situation is no different than what current small F9 payloads experience - such as CASSIOPE, DISCOVR, and now JASON-3 - and somehow those payloads don't seem to "liquefy". You are exaggerating the issue of g-loads at burnout.

I think that its not the same thing man. Running the numbers for a 110+ ton S2 lifted by 9 M-1ds to a 40 ton S2 lifted by one makes me think that the situation is different at S2 burnout with a small payload.

No, you are not getting what I'm saying. What I am proposing is that the upper stage basically be the F9 upper stage, but slimmed and stretched to F1 diameter, powered by a single M1D. This large upper stage would not have the burnout g-load issue that you are concerned with, since it would have a similar dry weight of the F9 upper stage. But since this stage would not be SSTO, I propose putting it on top of a smaller but same diameter 1st stage, with an M1D at full thrust.

This would be a real Frankenstein creation, but the the idea was to accomplish such a vehicle with existing SpaceX components.

Another option would be to have equal sized stages, but with the upper stage powered by an M1D at lowest thrust setting (~50%). The lower stage would run at full thrust.

[Dante80]

No, you are not getting what I'm saying. What I am proposing is that the upper stage basically be the F9 upper stage, but slimmed and stretched to F1 diameter, powered by a single M1D. This large upper stage would not have the burnout g-load issue that you are concerned with, since it would have a similar dry weight of the F9 upper stage. But since this stage would not be SSTO, I propose putting it on top of a smaller but same diameter 1st stage, with an M1D at full thrust.

But I understood what you said. That's why S2 is a little bigger than S1 (as you said), and it's less than half the weight of the F9 S2. The diameter is 1.7m.

edit: Oh, a second stage as big as the F9 S2 but taller and slimmer? If the second stage (same weight as F9 S2, less diameter) is put on top of a S1 with 1 M-1d, the M-1d cannot lift it I think.

[Lars-J]

But I understood what you said. That's why S2 is a little bigger than S1 (as you said), and it's less than half the weight of the F9 S2. The diameter is 1.7m.

No, you are still not getting what I mean. The diameter would be 1.7m, but it would contain almost the same amount of propellant as the F9 upper stage. It would be MUCH longer. And due to this non-optimal size, the dry mass of the stage would be the same or likely higher. Therefore no burnout g-load issue.

[Dante80]

The first stage would not lift it. It can't..the F9 S2 needs 9 M-1ds to lift it man. You are talking about a stage with about the same weight here...

The stage TWR of the MVac engine when starting in F9 is less than one (the engine can do 94,000kgf and the stage is 110,000kg+ at SEP). Now imagine replacing the MVac with a standard M-1d, add below it  another tank, and an engine with less thrust trying to lift it from the pad.

But since this stage would not be SSTO, I propose putting it on top of a smaller but same diameter 1st stage, with an M1D at full thrust.

I might have gotten this wrong, I don't understand (english is not my native language).