SpaceX Falcon Heavy Discussion (Thread 6)

[LouScheffer]

. Basically Falcon Heavy can accomplish the mission using a Star 48 in place of a Venus flyby gravity assist.

There isn’t one.  This is doing a Mars gravity assist

My understanding is that EC will be following a JUNO-like trajectory.  Juno went out to the orbit of Mars (or so), made a relatively small deep space maneuver (730 m/s) which set up a subsequent Earth flyby that provided the needed boost.  The advantage of doing it this way is that the spacecraft never gets much closer to the sun than Earth orbit (unlike a Venus gravity assist).  This makes the thermal problems much easier.

Clipper is doing the same thing, with the Mars flyby taking the place of the DSM.  Since Mars is light (as planets go) it cannot provide enough of a boost to send EC to Jupiter directly.  But it can provide enough delta-V to set EC up for an Earth flyby that does the hard work.

A Star-48 does not help much with Clipper, as Clipper is massive (6000 kg) compared to the Star 48 fuel (about 2000 kg).  So even a fully expended Falcon Heavy + Star-48 is not enough to send Clipper to Europa directly.  In theory, you could use FH to send EC+Star-48 out past the orbit of Mars, then use the Star-48 for the DSM, then do the Earth flyby as scheduled.  But this has a huge number of practical problems.  The Star-48 is not qualified for a 2 year long, very cold coast.  Plus to survive that long, EC would need to deploy its solar arrays, and the solar arrays are not qualified for forces that would result from a Star-48 firing.  So the Mars gravity assist is a better bet.

[yoram]

A Star-48 does not help much with Clipper, as Clipper is massive (6000 kg) compared to the Star 48 fuel (about 2000 kg).  So even a fully expended Falcon Heavy + Star-48 is not enough to send Clipper to Europa directly. 

Would a hypothetically scaled up Star-48 with more fuel be enough for a direct trajectory? Or would you run into the capacity limits of the Falcon Heavy?

[Robotbeat]

A Star-48 does not help much with Clipper, as Clipper is massive (6000 kg) compared to the Star 48 fuel (about 2000 kg).  So even a fully expended Falcon Heavy + Star-48 is not enough to send Clipper to Europa directly. 

Would a hypothetically scaled up Star-48 with more fuel be enough for a direct trajectory? Or would you run into the capacity limits of the Falcon Heavy?

There are other Star motor models.

[Paul451]

A Star-48 does not help much with Clipper, as Clipper is massive (6000 kg) compared to the Star 48 fuel (about 2000 kg).  So even a fully expended Falcon Heavy + Star-48 is not enough to send Clipper to Europa directly.

Would a hypothetically scaled up Star-48 with more fuel be enough for a direct trajectory? Or would you run into the capacity limits of the Falcon Heavy?

There are other Star motor models.

Any that have more than 2.4 tonnes of propellant, the upper limit of Star 48?

[joek]

Any that have more than 2.4 tonnes of propellant, the upper limit of Star 48?

Yes; see: https://www.northropgrumman.com/wp-content/uploads/NG-Propulsion-Products-Catalog.pdf

[Paul451]

Any that have more than 2.4 tonnes of propellant, the upper limit of Star 48?

Yes; see: https://www.northropgrumman.com/wp-content/uploads/NG-Propulsion-Products-Catalog.pdf

Did I need to qualify "In production"?

[joek]

Did I need to qualify "In production"?

You will need to take that up with NG as some are produced to order. In any case plenty of Star-48 (or Star-XX) variants that have >2.4t of propellant, which is what you asked.

[LouScheffer]

A Star-48 does not help much with Clipper, as Clipper is massive (6000 kg) compared to the Star 48 fuel (about 2000 kg).  So even a fully expended Falcon Heavy + Star-48 is not enough to send Clipper to Europa directly. 

Would a hypothetically scaled up Star-48 with more fuel be enough for a direct trajectory? Or would you run into the capacity limits of the Falcon Heavy?

To simplify the calculation, lets assume we need C3=80, Clipper = 6000 kg, and use hypothetical boosters that are multiples of the Star-48 (Full mass = 2141kg, empty mass 131 kg, ISP=292).  Delta-V is the dV imparted by the kick stage.  Mass is what the booster needs to lift, and C3 is the energy it needs to impart.  FH capacity is the mass that FH can lift to that C3, according to the NASA LSP site.   Ratio is the ratio what is needed to what FH can provide (so >1 means infeasible):

Kick stage  Delta-V  Mass C3 needed  FH capacity ratio
No Star 48       0   6000       80       2195    2.73
1x Star 48     811   8141     57.6       4375    1.86
2x Star 48    1419  10282     41.7       6400    1.61
4x Star 48    2298  14564     20.0      10115    1.43
8x Star 48    3400  23128       -5     ~16500    1.40

The table stops here since the NASA LSP site does not list capacity of FH to high elliptical orbits, which are ones with somewhat negative C3.  (Even the capacity for C3=-5 is slightly extrapolated.)  But it's pretty clear the benefit is flattening out, and no size of solid kick stage will work.

[Paul451]

Did I need to qualify "In production"?

Apparently I did. Okay, trying again:

Are there any larger variants of the Star motor that were manufactured in the current century, are flight rated and not unflown research projects, and thus could reasonably be considered to be "available" to NASA for the EC mission without them having to fund NG to restart a development program that was shut down a generation ago?

[Jim]

Did I need to qualify "In production"?

Apparently I did. Okay, trying again:

Are there any larger variants of the Star motor that were manufactured in the current century, are flight rated and not unflown research projects, and thus could reasonably be considered to be "available" to NASA for the EC mission without them having to fund NG to restart a development program that was shut down a generation ago?

Pegasus motors (Orion 50s) were looked at.

[alugobi]

Would SX ever put a rocket motor that they did not manufacture on one of their vehicles?

[abaddon]

Would SX ever put a rocket motor that they did not manufacture on one of their vehicles?

It would just be part of the payload, and yes.

[alugobi]

Part of the payload.  Ok, they'd do that.

[Tomness]

Did I need to qualify "In production"?

Apparently I did. Okay, trying again:

Are there any larger variants of the Star motor that were manufactured in the current century, are flight rated and not unflown research projects, and thus could reasonably be considered to be "available" to NASA for the EC mission without them having to fund NG to restart a development program that was shut down a generation ago?

Pegasus motors (Orion 50s) were looked at.

Would a Castor 30XL upper for Antares with Orion be able to fit in in Falcon Fairing and work?

[LouScheffer]

Are there any larger variants of the Star motor that were manufactured in the current century, are flight rated and not unflown research projects, and thus could reasonably be considered to be "available" to NASA for the EC mission without them having to fund NG to restart a development program that was shut down a generation ago?

Pegasus motors (Orion 50s) were looked at.

They may have been looked at, but ORION motors can be discarded as a possibility for direct-to-Jupiter pretty easily.  From the catalog, ORION 50S XLT (high performance, air start) masses 16221 kg at start, and 1121 kg at burnout.  Assuming an isp of 294 (IUS like) that's a delta V with a 6000 kg payload of 3279 m/s.  So for a final C3 of 80, you need the booster to give a C3 of -2.4 to a 22.2 ton payload.  But FH can only boost 16 tonnes to this C3 (LSP plot only goes to C3 = -1.7, but that's a very minor extrapolation).  So it's not even close.

[TrueBlueWitt]

Are there any larger variants of the Star motor that were manufactured in the current century, are flight rated and not unflown research projects, and thus could reasonably be considered to be "available" to NASA for the EC mission without them having to fund NG to restart a development program that was shut down a generation ago?

Pegasus motors (Orion 50s) were looked at.

They may have been looked at, but ORION motors can be discarded as a possibility for direct-to-Jupiter pretty easily.  From the catalog, ORION 50S XLT (high performance, air start) masses 16221 kg at start, and 1121 kg at burnout.  Assuming an isp of 294 (IUS like) that's a delta V with a 6000 kg payload of 3279 m/s.  So for a final C3 of 80, you need the booster to give a C3 of -2.4 to a 22.2 ton payload.  But FH can only boost 16 tonnes to this C3 (LSP plot only goes to C3 = -1.7, but that's a very minor extrapolation).  So it's not even close.

You also need a new(heavier) payload adapter for over 10,000 Kg.

Elon has said many times the easiest way to boost FH performance is to stretch the S2. He said they hadn't done it due to no previous missions needing it. Is this the one?

Can you close the gap doing this? How much of a stretch would it require?

For non-expendable FH and F9 this would also have a positive "knock-on" performance effect reducing S1 burnout velocity/apogee reducing residual prop required.

[LouScheffer]

Would a Castor 30XL upper for Antares with Orion be able to fit in in Falcon Fairing and work?

Whether or not it fits, it still falls slightly short of enough performance.  Taking the specs from the web site, 30XL mass is 26407 kg, empty mass is 1392 kg, and ISP is 294.4.  This gives a 6000 kg payload 4264 m/s.  So to get a direct-to-Jupiter C3 of 80, it would need to start with a C3 of -22.9 for a mass of 32.4 tonnes. 

The LSP calculator does not go below C3 = -1.7 for FH.  So we'll switch to the SpaceX website, which is MUCH more optimistic.  The two data points we have are LEO at 63,800 kg and GTO at 26,700 kg.  Assuming the LEO is 250 km circular (C3=-60.2) and GTO is 250x35768 km (C3=-16.35) then we can linearly interpolate (which will be optimistic - the curve is convex down).  Even with these optimistic assumptions, we still are slightly short (32.1 available vs 32.4 needed).

However, this is the closest I've seen to any FH + kick stage working for direct-to-Jupiter.

[Jim]

They may have been looked at, but ORION motors can be discarded as a possibility for direct-to-Jupiter pretty easily.

It never was for direct-to-Jupiter.  There was only one option for that.

And staged solids was looked at.

[LouScheffer]

Pegasus motors (Orion 50s) were looked at.

They may have been looked at, but ORION motors can be discarded as a possibility for direct-to-Jupiter pretty easily.  [...]

It never was for direct-to-Jupiter.  There was only one option for that.

What launcher/trajectory was looked at using an Orion 50?  Orion 50 + Europa Clipper combined mass 22.2t .   Atlas V can't even put this into LEO, and more than LEO is needed (LEO + Orion 50 won't even get to Earth escape).   The EMEJ trajectory they chose requires C3 = 42.  Subtract the Orion 50, and you get that you need to put 22.2t to a C3 of -31 (equivalent to a 12000 km apogee).  But according the LSP web site, VC6 can only put 17.8t to this apogee.  So unless LSP is very conservative, this won't work.

Aside from JUNO, there is other evidence LSP is conservative.  The original Europa Clipper trajectory (EVEEJ) called for C3 = 15 km^2/sec^2 from an Atlas 551.  But according to the NASA LSP, Atlas 5 can only deliver 4585 kg to this trajectory, whereas Clipper is specified at 6060 kg.  Did Clipper grow, or is LSP way conservative?

[Star One]

Are there any larger variants of the Star motor that were manufactured in the current century, are flight rated and not unflown research projects, and thus could reasonably be considered to be "available" to NASA for the EC mission without them having to fund NG to restart a development program that was shut down a generation ago?

Pegasus motors (Orion 50s) were looked at.

They may have been looked at, but ORION motors can be discarded as a possibility for direct-to-Jupiter pretty easily.  From the catalog, ORION 50S XLT (high performance, air start) masses 16221 kg at start, and 1121 kg at burnout.  Assuming an isp of 294 (IUS like) that's a delta V with a 6000 kg payload of 3279 m/s.  So for a final C3 of 80, you need the booster to give a C3 of -2.4 to a 22.2 ton payload.  But FH can only boost 16 tonnes to this C3 (LSP plot only goes to C3 = -1.7, but that's a very minor extrapolation).  So it's not even close.

You also need a new(heavier) payload adapter for over 10,000 Kg.

Elon has said many times the easiest way to boost FH performance is to stretch the S2. He said they hadn't done it due to no previous missions needing it. Is this the one?

Can you close the gap doing this? How much of a stretch would it require?

For non-expendable FH and F9 this would also have a positive "knock-on" performance effect reducing S1 burnout velocity/apogee reducing residual prop required.

I wondered that as I’ve seen a few people state that this mission will be flying with a stretched S2.