Spinner.
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?
Now, back to the question: what is better? What would you propose to do better?
Quote from: a_langwich on 10/15/2013 09:56 pmNow, 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.
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.
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.
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?
Quote from: a_langwich on 10/16/2013 06:56 amThat'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
Quote from: edkyle99 on 10/16/2013 02:01 pmAnother 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 KyleDoes a tank stretch really require an extensive development effort ?
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
Quote from: Lurker Steve on 10/16/2013 02:44 pmQuote from: edkyle99 on 10/16/2013 02:01 pmAnother 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 KyleDoes 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.
Does a tank stretch really require an extensive development effort ?