Author Topic: Can you beat a Star 48?  (Read 26500 times)

Offline a_langwich

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Can you beat a Star 48?
« on: 10/15/2013 09:56 pm »
The New Horizons Pluto mission used a Star 48 solid rocket.  Why would something that needed the maximum escape velocity use a low Isp solid?  Was there an extremely long period before restart?

Here are relevant numbers, for the Star 48B variant: 
(from http://www.atk.com/wp-content/uploads/2013/02/ATK-Motor-Catalog-2012.pdf )

Motor diameter:  49 inches
Motor length:      80 inches

(ie, there is plenty of room to grow width under a 4m or 5m shroud)

Effective specific impulse:  292.1 lbf-sec/lbm
Average thrust:             15,430 lbf

Total loaded weight:         4720.8 lbs
Total inert mass:                289.6 lbs

Propellant mass fraction:   0.94

One last, very important, "number" is that it has flown successfully enough times to raise its TRL to the coveted level of Boring. 


This isn't used to reach orbit, so I don't believe the thrust level is very critical.  Ion propulsion, for example, might be one of the competitors for some missions (specific energy would be its comparative metric).  What IS critical is maximum possible mass fraction at a reasonable total weight (that is, you can't assume unrealistic fuel loads to offset a heavy engine). 

Another very useful ability would be the ability to coast for more than a year before burning or between burns.

Isp is useful, but is actually LESS critical than empty weight or mass fraction.  Meaning that you need to gain a fairly substantial advantage in Isp in order to lose a small amount of mass fraction.


Now, back to the question:  what is better?  What would you propose to do better?
Is there a storable stage with better mass fraction?  or equal mass fraction but better Isp?  Could you do better with, say, propylene and LOX (~storable on-orbit)?  Is it better to go pressure-fed and ditch the weight of the pumps?  Or would they be okay if you just kept the engine size to 5,000 lbf or 10,000 lbf?

This seems like the size of problem that small new-space companies with expertise in propulsion could tackle, although vacuum testing might be a little challenge.  And, if they managed to fly a mission, a pretty lucrative market to play in.  Did I see an estimate of $30 million for a Star 48?  Is that way off?

Offline Danderman

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Re: Can you beat a Star 48?
« Reply #1 on: 10/15/2013 10:01 pm »
Spinner.

Offline a_langwich

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Re: Can you beat a Star 48?
« Reply #2 on: 10/15/2013 11:00 pm »
Spinner.


?  So? 

Can you beat a Star 48BV, which has a vectorable nozzle and 0.93 mass fraction?

Offline simonbp

Re: Can you beat a Star 48?
« Reply #3 on: 10/16/2013 12:04 am »
Well, Stars aren't perfect. The Star 30 on CONTOUR overheated and destroyed the spacecraft. That was a bit of concern, as New Horizons has a lot of structural and guidance heritage from CONTOUR.

As far as super high-TRL escape stages, the closest would be Agena, though it is no longer flying.

If you were building a new escape upper stage from scratch, I'm not sure what you would use. Hydrogen would have the most impulse, assuming there isn't too much boil-off. You could probably make a miniature version of the DCSS with a ~1-2.5 klb thrust engine contract-built by XCOR (RL-10 is ~10 klb). On the other hand, low density of LH2 might mean that CH4 is better, but I'm not sure if it would be worth it to go to longer-chain hydrocarbons.

It is interesting to think about, as the total amount impulse in a Star 30 is pretty similar to small VTVL rockets like Xombie or Morpheus, so this is not something you would need a massive industrial complex to build.

Offline Jim

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Re: Can you beat a Star 48?
« Reply #4 on: 10/16/2013 02:02 am »
The New Horizons Pluto mission used a Star 48 solid rocket.  Why would something that needed the maximum escape velocity use a low Isp solid?  Was there an extremely long period before restart?



No, it fired a right after separation.
Why was it used?
It is existed, it is cheap, it is simple and it is reliable.

And it will be used for Solar Probe Plus

Offline deltaV

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Re: Can you beat a Star 48?
« Reply #5 on: 10/16/2013 02:07 am »
Insulation doesn't scale down well (square/cube law). For that reason I'm skeptical of the merits of a hydrolox kick stage. A hypergolic stage would probably perform a bit better than solids due to better ISP. That doesn't mean they should switch to them since cost, not mass ratio, is the metric to optimize.

Offline LegendCJS

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Re: Can you beat a Star 48?
« Reply #6 on: 10/16/2013 02:14 am »
<my tagline here> ... not performance.   

$30 million for a Star 48 has to be way off, but I've no data to back this statement up.  If its true then I suggest changing the thread title by appending " for less that $30 million per unit cost."  Because there are going to be a lot of people who can think of ways of beating it on performance with money no object, and spending thought energy on that is a waste of time for all involved.
« Last Edit: 10/16/2013 02:33 am by LegendCJS »
Remember: if we want this whole space thing to work out we have to optimize for cost!

Offline Zed_Noir

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Re: Can you beat a Star 48?
« Reply #7 on: 10/16/2013 03:45 am »
How about an array of ion thrusters. With only one thruster being active at any time, rest for redundancy. Guess a tank of Xenon with the equivalent mass of the Star 48 will do a lot more. Of course it would be more complex and expensive.

Offline edkyle99

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Re: Can you beat a Star 48?
« Reply #8 on: 10/16/2013 04:19 am »
Now, back to the question:  what is better?  What would you propose to do better?
For this particular application (New Horizons), there really wasn't anything in the inventory that could do better, without, perhaps, swapping the entire payload to a Delta 4 Heavy (and even then I'm not sure).  No U.S. liquid stage currently exists that could perform this particular task, without stretching the Centaur on a one-off basis. 

Star 48, in several variations, has a long, proven history.  It began as PAM for Shuttle, then served as an upper stage for Delta 2.  It is being offered as an optional upper stage for Antares and for Minotaur 5 and 6.  It boosted LADEE on the inaugural Minotaur 5 launch recently.  It boosted Ulysses on its mission out of the ecliptic plane.  The Star 48 for New Horizons even beat that satellite to Jupiter! 

Smaller, but similar, spinning solid upper stage motors in the Star family have flown on Delta, Atlas, Titan, Japan's N-1, Thor (Burner), Scout, Vanguard, and likely some others that I've forgotten, not to mention serving as the kick motors for numerous satellites and as retro-motors for Gemini spacecraft.  There may be more spent Star motors still in orbit than active U.S. satellites (a guess).  All Star motors together may rival or surpass Agena as the most flown U.S. upper stage family.

 - Ed Kyle
« Last Edit: 10/16/2013 04:44 am by edkyle99 »

Offline cleonard

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Re: Can you beat a Star 48?
« Reply #9 on: 10/16/2013 06:26 am »
From an physics perspective the Star 48 is not the optimum.  When you get to actual engineering, it's can an item do what you need for the amount of dollars available with an acceptable risk.  In this case the Star 48 is the best compromise.

It's not all about ISP.  On the new horizons mission the Star 48 burn occurred pretty much right after the Centaur cutoff.  This allowed the burn to happen deep in Earth's gravity well.  The Oberth effect probably outweighed the greater ISP of a more traditional spacecraft hypergolic with relatively low thrust and long burn time.

Risk and overall cost were likely the driver for selecting the Star 48. 

The $30 million seems like a lot though.  There really isn't all that much to it.  I have a hard time seeing how it could cost more than $1 million to actually build it unless I'm discounting the costs of the avionics a bit to much.  Got to keep the people who do the building on the payroll and the associated management.

Offline a_langwich

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Re: Can you beat a Star 48?
« Reply #10 on: 10/16/2013 06:56 am »
Now, back to the question:  what is better?  What would you propose to do better?
For this particular application (New Horizons), there really wasn't anything in the inventory that could do better, without, perhaps, swapping the entire payload to a Delta 4 Heavy (and even then I'm not sure).  No U.S. liquid stage currently exists that could perform this particular task, without stretching the Centaur on a one-off basis. 

That's exactly what prompted the question:  if no US liquid stage currently existing could perform this particular task, what would such a stage look like?  Could better performance be had, or is this the best solution we can envision with current technology?  Is it just a matter of not having a storable in that size range, or can you not make a storable competitive with that?

If a probe were launched toward Pluto using an Ariane 5, what sort of kick stage would be used?
What about Proton?

I think the metric I'm looking for is total impulse per unit mass (of stage, not just fuel).  Would that be C3/kg?  deltaV/kg?  Or just a stage Isp?

Offline a_langwich

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Re: Can you beat a Star 48?
« Reply #11 on: 10/16/2013 07:22 am »
Insulation doesn't scale down well (square/cube law). For that reason I'm skeptical of the merits of a hydrolox kick stage. A hypergolic stage would probably perform a bit better than solids due to better ISP. That doesn't mean they should switch to them since cost, not mass ratio, is the metric to optimize.

I would agree cost is the metric to optimize, but for some of the outer planets missions, the budget is so mass constrained it would certainly be cost effective to consider more expensive stage options.  Notice they are using Atlas V 551; the next option up is a Delta 4 Heavy:  that's a very large dollar incentive to look for more energetic/lb kick stages.

And I don't get the sense that a Star 48 is priced anywhere near its production cost, or even cheap relative to first stage engines.  If it really is the only option, why should it be?  As I said, one document gave a WAG of $30 million, but that might have been for 2, and might have been completely uninformed.  Even at $5 million, I suspect a small new space company could produce a pretty ornate alternative at a profit.  Seems like a far more reasonable development project than a full orbital launch vehicle.
« Last Edit: 10/16/2013 07:31 am by a_langwich »

Offline Jim

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Re: Can you beat a Star 48?
« Reply #12 on: 10/16/2013 11:39 am »

 Even at $5 million, I suspect a small new space company could produce a pretty ornate alternative at a profit.  Seems like a far more reasonable development project than a full orbital launch vehicle.


No, not true.  The price of the Star-48 is fixed and there is little more to add to the cost for launch operations.  A new stage would cost a lot more than $5 million and it would require a lot of testing both ground and flight to qualify it for a mission.  Additionally, the costs to prepare it for a mission would be substantial (pressure test, prop loading equipment, prop loading team, etc)

Offline edkyle99

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Re: Can you beat a Star 48?
« Reply #13 on: 10/16/2013 02:01 pm »
That's exactly what prompted the question:  if no US liquid stage currently existing could perform this particular task, what would such a stage look like?  Could better performance be had, or is this the best solution we can envision with current technology?  Is it just a matter of not having a storable in that size range, or can you not make a storable competitive with that?
No U.S. storable (hypergolic) propellant stages are currently available in that total impulse class.  A storable stage able to perform this mission would probably end up weighing a little bit less than a Star 48B. 

Another option would be to fly a stretched Centaur.  Centaur would need to carry an extra 4.3 tonnes of propellant to provide the same delta-v as Star 48B for New Horizons.  That is a 20+% stretch, which would probably also require use of a dual engine Centaur.  Obviously, anything along these lines would require an extensive development effort.

 - Ed Kyle

Offline deltaV

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Re: Can you beat a Star 48?
« Reply #14 on: 10/16/2013 02:36 pm »
Astronautix gives a price of $4.060 million for PAM-S (http://www.astronautix.com/stages/pams.htm), a stage which includes a Star 48. That stage was used in the Ulysses solar probe, which was launched in 1990, so some inflation is in order. I'll take a WAG that a PAM-S would cost $6 million today. (I can't find the NASA new start index anywhere that isn't down due to the govt shutdown.)

Coincidentally SuperDraco is within a few percent of Star 48 in thrust. I wonder how much SpaceX would charge for a SuperDraco-based kick stage.

Offline Lurker Steve

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Re: Can you beat a Star 48?
« Reply #15 on: 10/16/2013 02:44 pm »
That's exactly what prompted the question:  if no US liquid stage currently existing could perform this particular task, what would such a stage look like?  Could better performance be had, or is this the best solution we can envision with current technology?  Is it just a matter of not having a storable in that size range, or can you not make a storable competitive with that?
No U.S. storable (hypergolic) propellant stages are currently available in that total impulse class.  A storable stage able to perform this mission would probably end up weighing a little bit less than a Star 48B. 

Another option would be to fly a stretched Centaur.  Centaur would need to carry an extra 4.3 tonnes of propellant to provide the same delta-v as Star 48B for New Horizons.  That is a 20+% stretch, which would probably also require use of a dual engine Centaur.  Obviously, anything along these lines would require an extensive development effort.

 - Ed Kyle

Does a tank stretch really require an extensive development effort ?

Offline LegendCJS

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Re: Can you beat a Star 48?
« Reply #16 on: 10/16/2013 03:42 pm »

Another option would be to fly a stretched Centaur.  Centaur would need to carry an extra 4.3 tonnes of propellant to provide the same delta-v as Star 48B for New Horizons.  That is a 20+% stretch, which would probably also require use of a dual engine Centaur.  Obviously, anything along these lines would require an extensive development effort.

 - Ed Kyle

Does a tank stretch really require an extensive development effort ?
Hmm, maybe you could see how long it took to complete a recent tank stretch effort moving a certain well known piece of space hardware from v1.0 to v1.1 to help answer this question.
Remember: if we want this whole space thing to work out we have to optimize for cost!

Offline ugordan

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Re: Can you beat a Star 48?
« Reply #17 on: 10/16/2013 05:45 pm »

Another option would be to fly a stretched Centaur.  Centaur would need to carry an extra 4.3 tonnes of propellant to provide the same delta-v as Star 48B for New Horizons.  That is a 20+% stretch, which would probably also require use of a dual engine Centaur.  Obviously, anything along these lines would require an extensive development effort.

 - Ed Kyle

Does a tank stretch really require an extensive development effort ?
Hmm, maybe you could see how long it took to complete a recent tank stretch effort moving a certain well known piece of space hardware from v1.0 to v1.1 to help answer this question.

You really think that was only a tank stretch job?

Offline Lurker Steve

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Re: Can you beat a Star 48?
« Reply #18 on: 10/16/2013 06:10 pm »
Let's list the things that DONT have to change, as opposed to that V1.1 upgrade.

Avionics remain the same
Engines remain the same
Inner stage adapter remains the same.
Plumbing between tanks and the RL 10 is pretty much unchanged, although some of the pipe lengths may vary slightly.
RCS/cold gas thrusters unchanged.
Payload adapter unchanged.
etc


Offline edkyle99

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Re: Can you beat a Star 48?
« Reply #19 on: 10/16/2013 06:16 pm »
Does a tank stretch really require an extensive development effort ?
Yes, because in this case a second RL10 would likely also have been needed, requiring development of Dual Engine Centaur.  But even just a tank stretch would require analysis and testing of its effects on flight stability and control during ascent and in-space use, on structural and bending mode issues, on the thermal effects of the longer RL10 burn, etc.  This would all be fine if it were being implemented for more than just one mission.

 - Ed Kyle
« Last Edit: 10/16/2013 06:19 pm by edkyle99 »

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