Why are the Star solid rocket motors still in use? The New Horizons probe used the Star 48, for example. And the Parker Solar Probe is also going to carry it.
They look extremely inconvenient and rudimentary. Low Isp, single-burn due to the use of solid fuel, ...
They are extremely inflexible, you configure it before the mission, and there's nothing you can do after that (you can not even regulate the thrust). It looks insane, to me that these things are used as upper stages.
It looks insane to me*
cheap and reliable I guess
Some times all you need is a kick in the pants to get into orbit
I don't know, something to be said for tried and true reliability.
Because its clearly the most badass way to go about getting into orbit.
>virgin liquid fuel rocket adjusts his thrust ratio until something goes wrong, at which point the liquid fuel and oxygen are cut off and the mission is aborted
>chad solid rocket booster rides his stick of highly flammable unstoppable controlled explosion all the way into motherfucking space, if a problem occurs he deflects it with his massive cock and keeps on flying away from Earth on his pile of burning doom.
Pretty sure that nuclear pulse propulsion is objectively the chadliest way you can move
Get's the job done and costs less.
Liquid fuels require a bunch of pumps and mechanical stuff. Solids are relatively simple and you don't have to worry about cryogenic or hypergolic fuels.
Ok you got me there.
They are a cheap, already developed and reliable means of providing a few km/s kick to a probe or satellite going somewhere.
They don't need to be fine tuned for putting payloads onto exact orbits, the missions that use them rely on them for 90-95% of a specific maneuver's delta V, then use the spacecraft itself for the last little bit because it's much more accurate.
They are flexible in the sense that they handle lots of different vibration and temperature conditions without issue, something not a lot of liquid stages can do.
Here's a perfectly reasonable use for a Star motor during a mission. Payload and Star motor are launched by an Atlas V to the Moon, on a trajectory that will put them over the south pole at an altitude of 500 km at periapsis. The Centaur upper stage has leftover propellants at engine shutdown, but they will boil away long before the payload reaches the Moon, so it separates. The payload coasts to the Moon and enters it Hill sphere, falling towards its closest point. Once the payload is a few seconds to reaching its periapsis it ignites its Star kick motor and decelerates, putting it onto a 500 km x 600 km polar orbit. The payload stages away the Star motor, which will eventually crash into the Moon as its orbit decays. The payload goes once around then uses its liquid thrusters to slow down a little more, ending up in a 500 km x 500 km circular, polar orbit.
Here's another use. A company wants to put a satellite at geostationary orbit but the rocket launch to go directly to GTO is $15 million more expensive than a rocket that will launch them into a low Earth orbit. Looking to save money, the company decides to use the smaller and cheaper launch vehicle as well as a Star kick motor to get to GTO, and use the payloads thrusters to get into geostationary orbit. This method saves the company several million dollars.
>nuclear pulse
>chadlier than the nuclear candle stick
nuh uh
they dont. its liquid. liquid hydrogen and liquid oxygen. watch footage of a rocket launch. especially the old stuff when people gave a shit about space. the stuff breaking away from the rocket is ice. that comes from the super cold fuel as both liquid hydrogen and liquid oxygen have to be super cold just to be in liquid state
in the mid 2000s they started syaing they used solid rocket fuel to try to throw off the chinese but china has better standardized test scores than america so this didnt work. china has their own space station
If that thing was full of hydrolox it wouldn't have more than 500m/s of dV lol
>in the mid 2000s they started syaing they used solid rocket fuel to try to throw off the chinese but china has better standardized test scores than america so this didnt work. china has their own space station
What the fuck are you on about?
Kick motors are extremely cheap and can be fitted in the space the payload would normally occupy. Developing an equivalent liquid third stage would take millions of dollars extra and years of time.
You do realize that rockets have stages and that some stages use different fuels right?
Also on the topic of rocket fuel, anyone else here hyped for the upcoming reprint of Ignition! ?
It would also be a lot bigger. Hydrogen takes up a lot of space.
cheeep
>anyone else here hyped for the upcoming reprint of Ignition! ?
Tue 15 May:
amazon.com
>The payload stages away the Star motor, which will eventually crash into the Moon as its orbit decays
Why would orbits around the Moon decay? Isn't the main reason for orbital decay atmospheric drag?
>Why would orbits around the Moon decay?
Because an orbit is you falling very very very very very slowly down a gravity well. Eventually you're going to hit the bottom.
>Because an orbit is you falling very very very very very slowly down a gravity well. Eventually you're going to hit the bottom.
No.
Gravitational stuff decays orbits too
Some reasons that cause orbits to decay:
1. Non-uniform concentrations of mass. Planets/moons are not perfect spheres. The changes in the gravitational attraction caused by these can slowly alter the orbit.
2. Tidal forces. If the orbiting body is massive enough, it can cause tides in the orbited body, altering the gravitational forces in the system. (This is not normally a problem for man-made objects, since they are way too small)
3. The influence of other bodies. Every mass in the solar system (and the universe) exerts gravitational force on all other masses. Of course, most of these masses/bodies are too far or are too small to have a significant impact for our purposes. You don't need to calculate Proxima Centauri's gravitation to go to the moon.
But in many situations, it is important to take this in account, and the influence of other bodies of the solar system are important.
In the case of a selenocentric orbit, the main 'actors' are: the Moon (of course), the Earth, and the Sun.
If you were to make a simulation to predict such lunar orbit, you would need to simulate these objects in it, if you wanted to get accurate predictions.
This problem is likely the main reason spacecrafts' orbits around the Moon are unstable.
Retard.
>2. Tidal forces. If the orbiting body is massive enough, it can cause tides in the orbited body, altering the gravitational forces in the system. (This is not normally a problem for man-made objects, since they are way too small)
Not the guy you replied to, but isn't the greater risk the fact that tidal forces would gradually pull apart the orbiting body if it entered the Roche limit? In effect, given enough time, the moon's gravity would destroy the spacecraft.
>This problem is likely the main reason spacecrafts' orbits around the Moon are unstable.
This post is pretty much 100% but I'd argue that reason 1 is the biggest contributor to shitty Moon orbits bc of a book I read once. They called them mascons and were pretty annoying for NASA during Apollo
>1. Non-uniform concentrations of mass. Planets/moons are not perfect spheres. The changes in the gravitational attraction caused by these can slowly alter the orbit.
en.wikipedia.org
There are surprisingly few stable lunar orbits. (at least at lower altitudes)
It's true though. Even in an ideal vacuum in a universe with only two perfect point masses, there'd be energy lost to gravitational waves, and an orbit would spiral in over time.
In real space, there's also drag because the vacuum is never perfect.
Aside from low orbits around a body with an atmosphere (such as Earth) normally third-body effects (any gravitational forces other than those that would be experienced between point masses, such as actual third bodies or mass irregularities that can be modelled as third bodies) are primarily responsible for orbital decay in practice, but that doesn't mean these other considerations aren't real.
They are relatively safe compared to liquid, also cheap and reliable.
Impulse density second to none easy to integrate to the stack and has stupidly low dry mass it is basically just a shell with nozzle stuck on top nothing to break there and small solids are efficient.
In the future something like adapted Electron Rutherford engine might be used from new kick stages because below some size liquid systems scale like shit.Star is 250kg while Centaur is over 20 t and it on the small side of hydrolox stages and are limited by on orbit life and are huge and without rebuilding a custom billion$+ centaur G you won't fit it in EELV fairing or you wait for New Glenn to lift that pig.
I am leaving any practical integration and dynamics problems for liquid kick stage aside because they make them nearly impossible to do in a reasonable way.
>stupidly low dry mass
Not really. They're alright, but nothing special. Star kick motors range from about 90-95% propellant by mass, like most upper stages.
>I am leaving any practical integration and dynamics problems for liquid kick stage aside because they make them nearly impossible to do in a reasonable way.
That's dumb. The basic alternatives are hydrazine monoprop or a hypergolic combination like MMH/NTO, both simply pressure fed. Either works well.
The main difference is, liquid-fuel kick motors are normally built into the spacecraft, rather than being a separate kick stage like the Star series. That way, the remaining propellant can be retained for general use, and the main thruster can be used for multiple burns. However, if you're doing a big one-time burn, a separate stage makes sense so you can drop that additional 5-10% mass of your initial propellant for the burn.
The Star stages are appreciated for their reliability. Solids have higher specific impulse than conventional monoprop spacecraft propulsion, but with comparable reliability. Hypergolic stages get a bit higher specific impulse than that, but are more complex and have a greater risk of something going wrong.
If someone put out the effort to develop and thoroughly test a series of small hypergolic stages until their reliability was impeccable, they'd likely be universally preferred over the Star stages for higher performance, lower vibration, and just generally being better. However, due to the simplicity of solids, it was cheaper to develop the Star motors to an adequate standard, and now they've got decades of practical use.
The Soviets didn't develop their solid rocket technology to nearly the same level, so they generally relied on hypergolic insertion stages (as do their Russian successors). I haven't heard of them going as small as the smallest Star motors, but for instance the smallest Fregat is roughly double the ~3 ton mass of Star 48.