kwan3217
Addon Developer
Space Shuttle Main Engines are expensive. They cost something like $50M each, which is justified only by the fact that they are re-used. On a shuttle-derived heavy lifter, three of these are thrown in the ocean.
So, I was looking into other hydrogen engines. We want hydrogen because we want this thing to be shuttle-derived. The best fit I have found so far is the RS-68 engine, used as the first stage engine in the Delta IV rocket.
First off, this thing is a beast. It has 50% more thrust than an SSME (3.4MN vs 2.2MN) so right off the bat we save one engine. Two RS-68s do the job of three SSMEs This also saves on the boattail, since it only has to house two engines and two sets of plumbing.
Secondly, these engines cost $14M for the standard Delta IV model or $20M for the human-rated version. A full set of engines for the cargo SDHLV costs about half as much as a single SSME. This saves something like $120M per launch.
However, there is a problem. RS-68 has a specific impulse of only about 410 seconds, quite a bit less than the SSME. We'll have to see how this affects payload to orbit.
One thing I am looking into but haven't found out yet is if the RS-68 needs an APU for hydraulics. The old F-1 engines on the Saturn V rockets uses their fuel as hydraulic fluid for controlling valves and actuating the thrust vector control. This is because its fuel was kerosene. I don't know about the J2 engines on the upper stage. The space shuttle uses an auxiliary power unit, a gas turbine engine which burns hydrazine and powers the hydraulic pumps. This makes sense because of the control surfaces, which need to be powered even when the main engines are not running. I would sure like to eliminate the APU system from SDHLV.
Next version soon, with a programmable autopilot actually useful for reaching a target orbit.
So, I was looking into other hydrogen engines. We want hydrogen because we want this thing to be shuttle-derived. The best fit I have found so far is the RS-68 engine, used as the first stage engine in the Delta IV rocket.
First off, this thing is a beast. It has 50% more thrust than an SSME (3.4MN vs 2.2MN) so right off the bat we save one engine. Two RS-68s do the job of three SSMEs This also saves on the boattail, since it only has to house two engines and two sets of plumbing.
Secondly, these engines cost $14M for the standard Delta IV model or $20M for the human-rated version. A full set of engines for the cargo SDHLV costs about half as much as a single SSME. This saves something like $120M per launch.
However, there is a problem. RS-68 has a specific impulse of only about 410 seconds, quite a bit less than the SSME. We'll have to see how this affects payload to orbit.
One thing I am looking into but haven't found out yet is if the RS-68 needs an APU for hydraulics. The old F-1 engines on the Saturn V rockets uses their fuel as hydraulic fluid for controlling valves and actuating the thrust vector control. This is because its fuel was kerosene. I don't know about the J2 engines on the upper stage. The space shuttle uses an auxiliary power unit, a gas turbine engine which burns hydrazine and powers the hydraulic pumps. This makes sense because of the control surfaces, which need to be powered even when the main engines are not running. I would sure like to eliminate the APU system from SDHLV.
Next version soon, with a programmable autopilot actually useful for reaching a target orbit.
