SpaceX Falcon Heavy Discussion (Thread 6)

[envy887]

Well, that's the difference. You presume FH cannot match SLS Block 1 capabilities. I posit that with Block 5 FH probably can, and Lou Scheffer's and Dr. Pietrobon's calculations agree. As far as I can tell neither LSP nor JPL have the numbers from SpaceX for Block 5 FH to do this comparison themselves.

See here for a good discussion
https://arstechnica.com/science/2018/04/if-were-really-going-to-europa-nasa-needs-to-pick-a-rocket-soon/?comments=1&post=35164983

I quoted that article above. That's the basis for my assertion that JPL doesn't have the FH Block 5 data to compare to SLS Block 1. Well, that plus Musk saying that LSP didn't have it either before the FH demo. The LSP website still shows pre-Block 5 data.

[RoboGoofers]

These are the kinds of trade-offs that need to be considered when choosing a LV and why it is good management to select a LV as soon as possible and not a good idea to switch horses in the middle of the race without a really good reason. Changing LV after the design is set causes all kinds of problems.

Many hundreds of millions of dollars is a good reason. With that kind of money we could do a EC2, or a Venus probe (or at least the preliminary budget estimate of one, and then drag the program out for a decade or two).

[FinalFrontier]

Well, that's the difference. You presume FH cannot match SLS Block 1 capabilities. I posit that with Block 5 FH probably can, and Lou Scheffer's and Dr. Pietrobon's calculations agree. As far as I can tell neither LSP nor JPL have the numbers from SpaceX for Block 5 FH to do this comparison themselves.

See here for a good discussion
https://arstechnica.com/science/2018/04/if-were-really-going-to-europa-nasa-needs-to-pick-a-rocket-soon/?comments=1&post=35164983

I quoted that article above. That's the basis for my assertion that JPL doesn't have the FH Block 5 data to compare to SLS Block 1. Well, that plus Musk saying that LSP didn't have it either before the FH demo. The LSP website still shows pre-Block 5 data.

SLS block 1 is a paper rocket that doesn't exist yet. It has not flown, any data sets available for it are no better.

In fact I would say they are even worse since at least FH Block 4 flew once already, so you have at least a starting point. We still have no idea what the exact real world performance will be for SLS.

And then there is the schedule. Is SLS even going to fly before 2020? We have a major 4 year election that year.

[Brovane]

Well, that's the difference. You presume FH cannot match SLS Block 1 capabilities. I posit that with Block 5 FH probably can, and Lou Scheffer's and Dr. Pietrobon's calculations agree. As far as I can tell neither LSP nor JPL have the numbers from SpaceX for Block 5 FH to do this comparison themselves.

See here for a good discussion
https://arstechnica.com/science/2018/04/if-were-really-going-to-europa-nasa-needs-to-pick-a-rocket-soon/?comments=1&post=35164983

I quoted that article above. That's the basis for my assertion that JPL doesn't have the FH Block 5 data to compare to SLS Block 1. Well, that plus Musk saying that LSP didn't have it either before the FH demo. The LSP website still shows pre-Block 5 data.

as Goldstein said figures for all the commercial rockets were provided by a competitor to SpaceX, United Launch Alliance.

Yup that sounds legit, let's go to ULA for performance on the FH.   

[LouScheffer]

The FH alone might do the job for Europa Clipper.  From the Space FH page it can put 63.8t into LEO.   Add in the second stage mass of 5t and that's a stack mass of 68.8t.   From LEO, a direct Jupiter path takes 6300 m/s.  That means a mass ratio of exp(6300/348/9.8 ) or 6.342, at the known ISP of 348.  So the ending stack mass is about 10.8t.  Subtract the 5t of the second stage to get a direct-to-Jupiter payload of 5.8t.  If the second stage is somewhat lighter, at 4.7t, as has been speculated, then the injected mass could well be 6.1t, the same as SLS (See This europa clipper presentation, page 31.), and exactly what Europa Clipper is designed for, so no spacecraft changes.

Sure, that's a completely expendable FH.  But it's still much cheaper than SLS, and much more capable than ATLAS.

Oops, I take that back.  It looks like Falcon Heavy is just a tad short of direct injection.  The difference is the actual delta-V being 100-200 m/s higher than I estimated, which makes a big difference at big delta-V.   I used the generic delta-v from Wikipedia, at 6300 m/s.  But NASA's trajectory browser says 6420-6540 m/s,  for real trajectories in the 2020s.  That makes a big difference.

Assuming it can put 63,800 kg into LEO, that's at least 68,000 kg on orbit.   Assuming ISP=348, then the burnout mass is determined by the delta V, then subtract the second stage (here estimated at 4.7t)  So for various delta-V

delta-V      burnout    payload
----------   ----------   ---------
6300 m/s  10723 kg   6023 kg
6400 m/s  10413 kg   5713 kg
6500 m/s  10112 kg   5412 kg
6600 m/s   9820 kg    5120 kg
6700 m/s   9536 kg    4836 kg
6800 m/s   9260 kg    4536 kg

So if Europa Clipper is indeed 6001 kg, FH is just short for all early 2020 trajectories.

There are two caveats to this conclusion, though.  One is that the same calculation gives very different number for Pluto than the SpaceX web site.  Wikipedia says 8200 m/s for Pluto.  That gives a burnout mass of 6143 kg, and hence a payload of only 1400 kg or so.  But the SpaceX site says 3500 kg, so something is odd.

The second caveat is that FH might work with a Mars gravity assist.  Mars is pretty light, as planets go, and does not help much.  But for asteroids, it can help by 20-30% in mass, which might be enough.  See Mars gravity assist to improve missions towards main-belt asteroids.  Now you might have to wait a bit longer (Mars should be in the right spot every 2 years, as opposed to once a year for Jupiter direct), but no thermal re-design would be needed (since no Venus flyby), and the flight time should remain short (close to the direct time) since the deflection at Mars is small.

[LouScheffer]

The second caveat is that FH might work with a Mars gravity assist.  Mars is pretty light, as planets go, and does not help much.  But for asteroids, it can help by 20-30% in mass, which might be enough.  See Mars gravity assist to improve missions towards main-belt asteroids.  Now you might have to wait a bit longer (Mars should be in the right spot every 2 years, as opposed to once a year for Jupiter direct), but no thermal re-design would be needed (since no Venus flyby), and the flight time should remain short (close to the direct time) since the deflection at Mars is small.

It looks like FH could do a Earth-Mars-Jupiter with a 6001 kg Europa clipper at many, but not all launch opportunities.   Here is a back of the envelope calculation showing this (it's a pretty large envelope).  Caveat: I've never done a gravity assist calculation before, so this is all from basic physics, and I may have made some horrible mistake.

Assume all orbits are circular.  Then the needed values are:
GM sun   1.327E+20
GM mars   4.280E+13
radius earth orbit   1.496E+11 m
radius mars orbit   2.270E+11 m
radius jupiter orbit   7.790E+11 m

To estimate the saving, first find the direct route.  A hohman transfer from Earth to Jupiter has
a = 4.643E+11 (semi-major access, average of both distances)
v = 38578 m/s at Earth, in heliocentric frame, using v=sqrt(GM*(2/r-1/a))
That is Earth circular velocity (29780 m/s) + 8795 m/s

Now do the flyby route.  Assume craft leaves Mars on Hohman trajectory.  The same calculation gives:
a = 5.030E+11
v = 30089 m/s at Mars distance (heliocnetric frame)
v = 24178 m/s, mars in its orbit (heliocnetric frame)
v = 5911  m/s,  velocity relative to Mars when leaving, tangent to orbit.

Now what angle can we turn through at Mars?  From Satellite Orbits - Gravitational Assist from Planets we see that the angle of deflection is 2*atan(GM/b/v^2).   We want the smallest possible b (distance from the planet) to get the biggest deflection, but we don't want to hit the planet.  I used 3600 km, since the radius of Mars is 3397 km.  Plugging in we find the angle of deflection is 0.655 radians, or 37.6 degrees.

Now we can find the incoming heliocentric velocity.  The tangential component is 24178 (mars) + 5911*cos(theta), and the radial component is 5911*sin(theta), for a total heliocentric velocity of 29086 m/s.   This shows we are on the right track, since the Earth-Jupiter direct has 29721 m/s as it crossed Mars orbit.

Now how much faster do we need to leave Earth to get this speed difference at Mars?  Working backwards, a v of 29086 m/s at Mars distance implies an orbit with a = 4.107E+11 m and a heliocentric speed at Earth of 38091 m/s.  This is a savings of 487 m/s, in the heliocentric frame.  We've reduced our Earth-relative velocity from 8795 m/s to 8308 m/s.

Now that we have the Earth-escape velocities, we need to convert them to delta-V from a low Earth orbit.  Using a 200 km orbit, and GM=3.986e14, we get Vcirc = 7784 m/s.  Now we can convert back to delta-V needed, from Vinfinity, using
delta-V = sqrt(Vinf^2+2*Vcirc^2) - Vcirc.
We get delta-V of 6306 m/s for direct to Jupiter, which is reassuring since that's a common estimate.
For the Mars flyby, we get delta-V = 6007 m/s, or 300 m/s better.

With a 300 m/s benefit, FH could launch a 6001 kg orbiter on many opportunities.  Assuming (as above) we need 6400 m/s or less after the benefit is applied, then using the NASA trajectory browser we could launch in 2021, 2022, 2023, 2027, or 2028.  Unfortunately the windows in 2024,2025, and 2026 remain just out of reach.  Clearly these cases are so close to the edge that a more detailed analysis would be required to get a serious answer.

EDIT: fixed sign error in explanation.  Math still the same.

[lrk]

Has any thought been given to putting a solid-fueled kick stage on top of Falcon Heavy (as with what the Parker Solar Probe is doing?)  If FH by itself comes close, could adding a kick stage be enough to get EC direct to Jupiter? 

Alternatively, what about just giving the probe itself a large dV capability (similar to GEO comsats that must insert themselves from GTO?) 

[speedevil]

Oops, I take that back.  It looks like Falcon Heavy is just a tad short of direct injection.  The difference is the actual delta-V being 100-200 m/s higher than I estimated, which makes a big difference at big delta-V.   I used the generic delta-v from Wikipedia, at 6300 m/s.  But NASA's trajectory browser says 6420-6540 m/s,  for real trajectories in the 2020s.  That makes a big difference.

Assuming it can put 63,800 kg into LEO, that's at least 68,000 kg on orbit.   Assuming ISP=348, then the burnout mass is determined by the delta V, then subtract the second stage (here estimated at 4.7t)  So for various delta-V
<snip>
6800 m/s   9260 kg    4536 kg

So if Europa Clipper is indeed 6001 kg, FH is just short for all early 2020 trajectories.

There are two caveats to this conclusion, though.  One is that the same calculation gives very different number for Pluto than the SpaceX web site.  Wikipedia says 8200 m/s for Pluto.  That gives a burnout mass of 6143 kg, and hence a payload of only 1400 kg or so.  But the SpaceX site says 3500 kg, so something is odd.

Not quoting the tweet I've mentioned from Elon about the second stage being the easiest one to stretch.

Naively, it seems a 50% or so stretch on the second stage, while having perhaps 300m/s impact on the first stage should easily make up the difference and a little more, enabling 6 tons to the full velocity.

[envy887]

Has any thought been given to putting a solid-fueled kick stage on top of Falcon Heavy (as with what the Parker Solar Probe is doing?)  If FH by itself comes close, could adding a kick stage be enough to get EC direct to Jupiter? 

Alternatively, what about just giving the probe itself a large dV capability (similar to GEO comsats that must insert themselves from GTO?)

Yes. JPL was modeling a (probably) non-Block 5 FH with a solid kick stage, and it could not match SLS Block 1. However, Block 5 is likely very close to SLS Block 1, and with a kick stage can probably match it.

Oops, I take that back.  It looks like Falcon Heavy is just a tad short of direct injection.  The difference is the actual delta-V being 100-200 m/s higher than I estimated, which makes a big difference at big delta-V.   I used the generic delta-v from Wikipedia, at 6300 m/s.  But NASA's trajectory browser says 6420-6540 m/s,  for real trajectories in the 2020s.  That makes a big difference.

Assuming it can put 63,800 kg into LEO, that's at least 68,000 kg on orbit.   Assuming ISP=348, then the burnout mass is determined by the delta V, then subtract the second stage (here estimated at 4.7t)  So for various delta-V
<snip>
6800 m/s   9260 kg    4536 kg

So if Europa Clipper is indeed 6001 kg, FH is just short for all early 2020 trajectories.

There are two caveats to this conclusion, though.  One is that the same calculation gives very different number for Pluto than the SpaceX web site.  Wikipedia says 8200 m/s for Pluto.  That gives a burnout mass of 6143 kg, and hence a payload of only 1400 kg or so.  But the SpaceX site says 3500 kg, so something is odd.

Not quoting the tweet I've mentioned from Elon about the second stage being the easiest one to stretch.

Naively, it seems a 50% or so stretch on the second stage, while having perhaps 300m/s impact on the first stage should easily make up the difference and a little more, enabling 6 tons to the full velocity.

The kick stage is probably a lot easier and cheaper for a one-off mission. It sheds almost 5 tonnes off the final the burnout mass. A STAR-48 adds between 1 tonne and 1.5 tonnes to the payload to C3=80 km²/s²

[Jim]

STAR-48 is too small

[ugordan]

And really, is it worth the hassle of integrating a smallish kick stage and doing additional analysis on thermal, loads, vibrationm, etc. on the spacecraft instead of just using a Juno-like trajectory - injecting into a heliocentric orbit with around a 2 year period and using one Earth flyby for the final injection. That should be doable by both D-IVH and FH and all the more if SLS ends up being delayed by the same amount of time over when the EC is actually ready to fly.

[LouScheffer]

And really, is it worth the hassle of integrating a smallish kick stage and doing additional analysis on thermal, loads, vibrationm, etc. on the spacecraft instead of just using a Juno-like trajectory - injecting into a heliocentric orbit with around a 2 year period and using one Earth flyby for the final injection. That should be doable by both D-IVH and FH and all the more if SLS ends up being delayed by the same amount of time over when the EC is actually ready to fly.

I don't think this particular trajectory makes sense.  It requires a deep space maneuver of about 800 m/s, which is leveraged to gain about 3000 m/s through the flyby.   But in the Europa Clipper - FH case, it's already within 800 m/s of what they need.  So if EC could do the Juno path, it could also simply add 800 m/s to the launch speed and get direct to Jupiter.

[AncientU]

And really, is it worth the hassle of integrating a smallish kick stage and doing additional analysis on thermal, loads, vibrationm, etc. on the spacecraft instead of just using a Juno-like trajectory - injecting into a heliocentric orbit with around a 2 year period and using one Earth flyby for the final injection. That should be doable by both D-IVH and FH and all the more if SLS ends up being delayed by the same amount of time over when the EC is actually ready to fly.

I don't think this particular trajectory makes sense.  It requires a deep space maneuver of about 800 m/s, which is leveraged to gain about 3000 m/s through the flyby.   But in the Europa Clipper - FH case, it's already within 800 m/s of what they need.  So if EC could do the Juno path, it could also simply add 800 m/s to the launch speed and get direct to Jupiter.

For the difference in cost between FH and DIVH*, FH could have a methalox second stage.  That would solve the delta-v problem quite nicely.


* or a small fraction of the difference with SLS

[envy887]

And really, is it worth the hassle of integrating a smallish kick stage and doing additional analysis on thermal, loads, vibrationm, etc. on the spacecraft instead of just using a Juno-like trajectory - injecting into a heliocentric orbit with around a 2 year period and using one Earth flyby for the final injection. That should be doable by both D-IVH and FH and all the more if SLS ends up being delayed by the same amount of time over when the EC is actually ready to fly.

Then you need to do the analysis of what two extra years of flight time will do.

STAR-48 is too small

To small for what? To get pre-Block 5 FH into SLS Block 1 payload range? That seems likely. But an extra 1 to 1.5 tonnes on top of what Block 5 FH can do should be big enough.

[LouScheffer]

STAR-48 is too small

To back up this statement:
Star 48B masses about 2000kg, and supplies 591,000 kg(force)seconds. So if we add this to a 6000 kg probe, the starting mass will be 8000 kg and the ending about 6000 kg.  With an ISP of 292, this gives a delta-V of 292*9.8*ln(8/6) = 823 m/s.

But the extra mass takes performance from the second stage, which now ends at 13t, instead of 11t.  The loss is 348*9.8*ln(13/11) = 570 m/s.

So the net gain is only 823-570 = 253 m/s.  That's not enough to erase the shortfall at all launch opportunities, though it would help for some, since the FH is pretty close already. 

[envy887]

The FH alone might do the job for Europa Clipper.  From the Space FH page it can put 63.8t into LEO.   Add in the second stage mass of 5t and that's a stack mass of 68.8t.   From LEO, a direct Jupiter path takes 6300 m/s.  That means a mass ratio of exp(6300/348/9.8 ) or 6.342, at the known ISP of 348.  So the ending stack mass is about 10.8t.  Subtract the 5t of the second stage to get a direct-to-Jupiter payload of 5.8t.  If the second stage is somewhat lighter, at 4.7t, as has been speculated, then the injected mass could well be 6.1t, the same as SLS (See This europa clipper presentation, page 31.), and exactly what Europa Clipper is designed for, so no spacecraft changes.

Sure, that's a completely expendable FH.  But it's still much cheaper than SLS, and much more capable than ATLAS.

Oops, I take that back.  It looks like Falcon Heavy is just a tad short of direct injection.  The difference is the actual delta-V being 100-200 m/s higher than I estimated, which makes a big difference at big delta-V.   I used the generic delta-v from Wikipedia, at 6300 m/s.  But NASA's trajectory browser says 6420-6540 m/s,  for real trajectories in the 2020s.  That makes a big difference.

Assuming it can put 63,800 kg into LEO, that's at least 68,000 kg on orbit.   Assuming ISP=348, then the burnout mass is determined by the delta V, then subtract the second stage (here estimated at 4.7t)  So for various delta-V

delta-V      burnout    payload
----------   ----------   ---------
6300 m/s  10723 kg   6023 kg
6400 m/s  10413 kg   5713 kg
6500 m/s  10112 kg   5412 kg
6600 m/s   9820 kg    5120 kg
6700 m/s   9536 kg    4836 kg
6800 m/s   9260 kg    4536 kg

So if Europa Clipper is indeed 6001 kg, FH is just short for all early 2020 trajectories.

There are two caveats to this conclusion, though.  One is that the same calculation gives very different number for Pluto than the SpaceX web site.  Wikipedia says 8200 m/s for Pluto.  That gives a burnout mass of 6143 kg, and hence a payload of only 1400 kg or so.  But the SpaceX site says 3500 kg, so something is odd.

The second caveat is that FH might work with a Mars gravity assist.  Mars is pretty light, as planets go, and does not help much.  But for asteroids, it can help by 20-30% in mass, which might be enough.  See Mars gravity assist to improve missions towards main-belt asteroids.  Now you might have to wait a bit longer (Mars should be in the right spot every 2 years, as opposed to once a year for Jupiter direct), but no thermal re-design would be needed (since no Venus flyby), and the flight time should remain short (close to the direct time) since the deflection at Mars is small.

Are there two Clipper mass targets? Atlas V can only put 4500 kg to the VEEGA trajectory, and this slide gives a 41% mass margin indicating a 3200 kg payload. SLS can put 6100 kg direct to TJI, and this shows a 45% mass margin indicating a 4200 kg payload.

FH can most probably put more mass direct to Jupiter than Atlas V 551 can put to VEEGA.

[Tomness]

STAR-48 is too small

To back up this statement:
Star 48B masses about 2000kg, and supplies 591,000 kg(force)seconds. So if we add this to a 6000 kg probe, the starting mass will be 8000 kg and the ending about 6000 kg.  With an ISP of 292, this gives a delta-V of 292*9.8*ln(8/6) = 823 m/s.

But the extra mass takes performance from the second stage, which now ends at 13t, instead of 11t.  The loss is 348*9.8*ln(13/11) = 570 m/s.

So the net gain is only 823-570 = 253 m/s.  That's not enough to erase the shortfall at all launch opportunities, though it would help for some, since the FH is pretty close already.

What about Star 48GXV tested for the Parker Solar Probe mission as the upper stage on a Atlas V 551 vehicle but was cancelled in favor of DIVH
 cited Wiki via Orbital ATK

[russianhalo117]

STAR-48 is too small

To back up this statement:
Star 48B masses about 2000kg, and supplies 591,000 kg(force)seconds. So if we add this to a 6000 kg probe, the starting mass will be 8000 kg and the ending about 6000 kg.  With an ISP of 292, this gives a delta-V of 292*9.8*ln(8/6) = 823 m/s.

But the extra mass takes performance from the second stage, which now ends at 13t, instead of 11t.  The loss is 348*9.8*ln(13/11) = 570 m/s.

So the net gain is only 823-570 = 253 m/s.  That's not enough to erase the shortfall at all launch opportunities, though it would help for some, since the FH is pretty close already. 

Star-48 is to small and intended for small high energy payloads. Castor-30, Star-75 and Star-92 series are more suited for this roll as a replacement to legacy kick motors that are no longer available

[russianhalo117]

STAR-48 is too small

To back up this statement:
Star 48B masses about 2000kg, and supplies 591,000 kg(force)seconds. So if we add this to a 6000 kg probe, the starting mass will be 8000 kg and the ending about 6000 kg.  With an ISP of 292, this gives a delta-V of 292*9.8*ln(8/6) = 823 m/s.

But the extra mass takes performance from the second stage, which now ends at 13t, instead of 11t.  The loss is 348*9.8*ln(13/11) = 570 m/s.

So the net gain is only 823-570 = 253 m/s.  That's not enough to erase the shortfall at all launch opportunities, though it would help for some, since the FH is pretty close already.

What about Star 48GXV tested for the Parker Solar Probe mission as the upper stage on a Atlas V 551 vehicle but was cancelled in favor of DIVH
 cited Wiki via Orbital ATK

Star 48GXV never completed development and is not available at this time.

[fthomassy]

Is not the time of flight -70%?