The way you ignite a rocket engine depends a lot on the fuel/oxidiser combination. Some combinations, like Liquid Hydrogen/Liquid Oxygen (HydroLox) ignite very easily and are ignited using a glorified spark plug (this is the case of the RL10, used on the Centaur Upper Stage). The RP1 (Kerosene)/Liquid Oxygen mixture is harder to ignite, and requires more ...
It was impossible to restart the engines in flight.
If for no other reason, the pressure/temperature conditions for the "start box"1 were not met in flight. Also, Post Shutdown to Engine Ready was not a legal transition in the controller flight software. There were also considerations of engine drying (removal of residual water after shutdown), prelaunch ...
Per this old usenet thread, there are a lot of design choices, but the main problems are in getting the fuel to the engines while in free-fall, and igniting non-hypergolic propellants.
To get the fuel into the pumps / engines, you can use:
bladder pressurization (which is a materials problem with cryo fuels)
piston pressurization (difficult to do on a ...
Basing on two papers I had managed to find: Electrical Solid Propellants:
A Safe, Micro to Macro Propulsion Technology and Plasma Plume Characterization of Electric Solid Propellant Pulsed Microthrusters.
First, the concept isn't new; it's an incremental research on Pulsed Plasma Thrusters which were used first on soviet Zond 2 and Zond 3, starting in ...
The Merlin engines are ignited with a mixture of triethylaluminium and triethylborane (TEA-TEB); according to Wikipedia:
Triethylborane is strongly pyrophoric, igniting spontaneously in air, burning with an apple-green flame characteristic for boron compounds. Thus, it must be handled and stored in nitrogen or argon.
The green colour is characteristic of TEB (Triethylborane) combustion, which is used in combination with TEA (Triethylaluminum) to ignite the Merlin 1D engines (those two substances are hypergolic, and are used to kickstart the RP1/Oxygen combustion).
At least three of the nine engines are equipped with an onboard supply of TEA-TEB for in-flight relights. ...
My understanding is that designing for multiple restarts isn't particularly difficult; it's just that most engines don't have the need for it, so they don't bother.
The RL-10 mentioned in the Lunar COTS paper you linked has been restarted at least 7 times in a single real mission, and depending on the model, is rated for 10 starts and 4000 seconds of run ...
For liquid hydrogen / liquid oxygen rocket engines, O2 rich cutoff is disastrous. Extra H2 was loaded into the shuttle's external tank to ensure that small performance problems or analysis errors would not result in an O2 rich cutoff. This was referred to as the "fuel bias". On a nominal day, this extra fuel was carried to orbit, wasting payload capability,...
This occurs in the very last moments before the engine is shut down. In fact, as you mentioned, the acceleration drops to 0 as this happens. There's a number of possible explanations, including:
The engine had a slight gimbal that was reverted upon completion of the thrust.
There isn't any real movement, but rather the difference in the sun angle to re-...
"On The Shoulders of Titans" suggests that the oxidizer leakage was simply the natural outcome of allowing the oxidizer to flow into the (open-ended) combustion chamber prior to the fuel:
The problem was rooted in NASA's original specification for a Gemini target vehicle able to start and stop its main engine five times during a mission, in contrast to ...
When the results of the experiment become public, they should become visible on the NASA page you linked to. I haven't found anything in NTRS or on the website of the Naval Research Laboratory that runs the experiment.
Spinsat was launched from the ISS on Nov. 28, 2014.
This page has some details on what happened after launch:
• Sept. 2015: Already in ...
For the purposes of your question, I will subdivide rocket engine designs into two categories, and some sub-categories
Designs using hypergolic propellants
Designs using non-hypergolic propellants
Designs using a torch igniter or something similar
Designs using non-reusable ignition mechanisms (e.g. hypergolic slugs, solid fuel igniters, probably others I ...
This is an engine still in development, so I believe that means the throttle range varies with the test configuration, from 3:1 (i.e. if maximum throttle is 100% thrust, minimum is 33% thrust) to 5:1 (20%-100%).
Supplemental to Organic Marble's answer:
Additional questions include: 1) Is the RL10B-2 used as a testbed for the CECE? Are the CECE, physical dimension the same as the as the RL10B-2?
The RL10B-2 uses an 2-piece extensible sliding nozzle to get an extremely high nozzle expansion ratio of 280:1 and consequent specific impulse of 465 seconds. The CECE ...
Upper stage engines used or planned for human cargo:
RL10 / Atlas 5 & ICPS & EUS / Good performance (Isp > 400)
RD-110 / Soyuz / OK performance (Isp > 300)
Merlin / Falcon / OK performance (Isp > 300)
YF-25 / Long March / Poor performance (Isp > 200)
(I probably forgot something)
(Source Wikipedia various)
The CECE testbed seems to have been ...
Perhaps there's some confusion in the terminology? At least for the Space Shuttle Main Engine, the Augmented Spark Igniters didn't fire for the whole burn.
The igniters turn off after 4.4 seconds while the ignition
flame continues in order to prevent intermittent and possibly
damaging blowback from the main combustion area. This also ...
Both the J-2 engine used on the Saturn V and the RL-10 used on the Centaur and DCSS upper stages are hydrogen-fueled and restartable.
The Saturn V third stage burned once to finish insertion into low Earth orbit, once to send the Apollo
spacecraft on its way to the moon, and once for its final disposition, either to hit the moon or to go into solar orbit.
There may be others, but at least the Saturn 5's J2 engines have a operational history of inflight restarts (from wikipedia)
Unlike most liquid-fuelled rocket engines in service at the time, the
J-2 was designed to be restarted once after shutdown when flown on the
Saturn V S-IVB third stage. The first burn, lasting about two minutes,
placed the ...
The design shown in the patent application doesn't look typical of common IC engines; I'll guess it was an idea someone had that may or may not be a real improvement. Engines I am familiar with have no such pre-chamber; the spark fires in the "main" combustion chamber, but I don't think that's relevant to the question.
The NASA device looks like it's ...
There is no SENSIBLE upper limit in terms of the likely requirements in the next few decades. Increasing restart capability adds complexity and a certain amount of mass but you can soon get to a system which is essentially reliability limited. Tens to hundreds of restarts would readily be achievable with existing technology.
As one only example
You can ...