Groan. Worst kind of pedant.

It's also what the main boosters of the shuttle system did.

The combustion process adds significant velocity to the propellant when properly nozzled. What is the point of adding the danger of a nuclear energy source in space when the propellant is completely expended? Just use chemistry.

Nope. This test was a proof of concept engine. The next version will be a fully functional engine that they can measure specific impulse, thrust, and engine life for.

Nuclear rockets use pure hydrogen as propellant. Lighter molecules move faster, and H2 is much lighter than H2O.

Map showing location of exoplanets. Most are within 5000 light years. Gravitational lensing allows astronomers to see a few in the direction of the galactic center.

As I recall, astronomers may have detected one exoplanet in the Magellanic Clouds.

> You can't just heat up water and shoot it out the back,

That's exactly what the third stage of the Artemis I rocket did on Nov 16th. Except the water was carried as separate hydrogen and oxygen tanks, and burning them is what produces the heat. What comes out the nozzle is superheated steam.

Integza has a really neat video about RDE, and in addition to going over some of the science behind it, he makes a homemade one. It's very cool.

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Really?? I had no add at all. Ublock origin seems to do his work.

I dunno...

I for one welcome Arty the Asteroid to Earth.

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:

|Fewer Letters|More Letters| |-------|---------|---| |DARPA|(Defense) Advanced Research Projects Agency, DoD| |DoD|US Department of Defense| |FFSC|Full-Flow Staged Combustion| |H2|Molecular hydrogen| | |Second half of the year/month| |HEU|Highly-Enriched Uranium, fissile material with a high percentage of U-235 ("boom stuff")| |Isp|Specific impulse (as explained by Scott Manley on YouTube)| | |Internet Service Provider| |LH2|Liquid Hydrogen| |NTR|Nuclear Thermal Rocket| |SSTO|Single Stage to Orbit| | |Supersynchronous Transfer Orbit|

|Jargon|Definition| |-------|---------|---| |EMdrive|Prototype-stage reactionless propulsion drive, using an asymmetrical resonant chamber and microwaves| |hydrolox|Portmanteau: liquid hydrogen fuel, liquid oxygen oxidizer| |turbopump|High-pressure turbine-driven propellant pump connected to a rocket combustion chamber; raises chamber pressure, and thrust|

^(11 acronyms in this thread; )^(the most compressed thread commented on today)^( has 15 acronyms.)
^([Thread #8497 for this sub, first seen 30th Jan 2023, 16:09]) ^[FAQ] ^([Full list]) ^[Contact] ^([Source code])

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Note that this is because those are gigantic worlds that’s still glowing brightly from the heat they obtained from their very recent formation (these directly imaged planets are usually a few tens of million years old). We should be able to image not-visibly-glowing planets soon, but not as of today.

The Solar System is too old for anything but the Sun to glow (except collisions which are extremely rare too), and brightness of Solar System objects scale to distance to the power of four (2 from dimming sunlight, 2 from the distance itself), so any cold planet rapidly fades into invisibility.

That's not how rockets work. Vehicle speed changes as your run the engine and produce thrust (push). Earth and Mars already are in orbit around the Sun. To get to Mars, you have to change your orbit so the other end crosses Mars' orbit at the same time Mars is at that point.

We can't actually see the exoplanets directly.

What we see is a slight dimming of the star it's orbiting as it passes between the star and us. Imagine someone walking in front of a car with it's headlights on while at night. You can see the change in the light, but it's unlikely you can see the person. Same principle.

We can then look at how the star "wobbles" in it's orbit. That gives us an idea of how much mass the planet has.

As a bonus: With the right tools, we can look at the light just as it starts to dim and this will give us an idea of what the atmosphere is comprised up.

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I thought that too until recently, but it's simply not true. In fact, we've been directly imaging exoplanets for over a decade.

https://www.reddit.com/r/Damnthatsinteresting/comments/q6u9bj/four_exoplanets_orbiting_the_star_hr8799_directly/

https://en.wikipedia.org/wiki/List_of_directly_imaged_exoplanets

In theory the RDRE would improve chemical rocket efficiency by about 10%. There is a finite amount of energy in any fuel/oxidizer combination set by the chemistry. Regular rocket engines use a turbopump to push the ingredients into a combustion chamber at high pressure. The expansion of the resulting hot gas is what turns into thrust.

The RDRE feeds the ingredients at lower pressure, and uses a detonation to create the high pressure for expansion. The energy otherwise used to run the turbopumps is then directly used for thrust. Turbopumps generally tap off some of the fuel and oxidizer flow to power themselves.

Scott Manley did a really good video on RDE propulsion. Definitely worth a watch.

Well, we have seen explanets directly. Just not most.

Well, we have imaged a couple dozen exoplanets directly. But we'd see those ones if they were in the Solar system too.

We can't see exoplanets directly. We see the effect their atmospheres have on the light that passes through them, and we see the gravitational effects the planets have on their parent star in the form of the stars' "wobble". There are no direct images of exoplanets.

Edit: I stand corrected. We have directly imaged exoplanets

If we knew exactly where to look, we probably could just barely see dwarf planets or even bigger ones in the Kuiper belt. It's hard to pick them out from the background noise when they're so dim and far from the sun.