Aantares
Space exploration

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12-07-2020, 05:59 PM
Henry J
Space exploration
It's interesting that they think fusion rockets would be good for the long trips, but not so much for the ground to orbit and back trips. The two reasons for that are cost, and neutrons.

The cost of manufacturing a fusion rocket is expected to be rather high, especially a big one. And getting a vehicle off the ground would take several of them, whereas for interplantetary travel, they can use low acceleration at each end of the trip, so one or two small engines would be enough.

Then there's the neutrons - not from the primary fusion that is expected to provide the most push, but from a secondary reaction. So it's a low level of neutrons, but still not wanted in an area one cares about.
12-16-2020, 11:19 AM
Henry J
Found a report on status of the fusion rocket research. The parts that aren't over my head are fascinating.

https://www.nasa.gov/sites/def...propulsiontagged.pdf
12-16-2020, 12:09 PM
Henry J
On reading a bit more of it, that pdf was talking about using dueterium and tritium for fusion (H2 and H3) rather than the dueterium and helium (H2 and He3) that the articles I read earlier were talking about. And, the report was for 2012-2015, and some of the articles were more recent.
12-16-2020, 12:49 PM
Henry J
Ah so. Maybe I just realized why they'd switch from using H3 (tritium) to using He3 (helium-3), when on Earth H3 is easier to find than He3, and easier to fuse with H2 (deuterium).

But H3 decays over time, with a half life of 12 days. Which means that for each gram of it that they'd need 210 days later, they'd have to start out with several million g (thousands of kg) of the stuff.
12-17-2020, 01:25 PM
Henry J
One interesting thing with fusion rockets is that while the amount of fusion fuel needed is tiny, it still needs a large amount of propellant for an interplanetary trip.

For the 7 month round trip to Mars, they expect to use less than a kg of H2 and He3, but the lithium propellant starts out as more than a third of the ship's mass at the start of the trip.

And while they could theoretically get from Earth to Mars in a month, that would require refueling (with lithium) at the other end, which would mean sending a supply in a separate launch ahead of time.
12-19-2020, 07:16 PM
Henry J
I found a table in that article that gives the delta-V for each of the four manuevers in the 7 monty round trip. It adds up to about 50 km/sec, and that's with a single stage vehicle

Whereas with chemical rockets, it takes three stages to produce 10 km/sec (7 miles/sec) in a launch from Earth.

(delta-V is change of speed produced by firing of the rockets.)
01-29-2021, 09:29 PM
Henry J
NASA’s Perseverance Rover 22 Days From Mars Landing

https://www.nasa.gov/feature/j...ys-from-mars-landing
02-18-2021, 11:05 AM
Henry J
Perserverance landing is this afternoon
02-18-2021, 03:47 PM
Henry J
It hath landed!
02-26-2021, 03:25 PM
Henry J
Maybe discussions about Mars (or other planets) should be here instead of there! Since there has gone sort of downhill.
03-01-2021, 11:32 AM
Ictalurus Punctatus
quote:
Originally posted by Henry J:
Maybe discussions about Mars (or other planets) should be here instead of there! Since there has gone sort of downhill.

I agree
03-03-2021, 04:38 PM
Henry J
Some pictures from the one that Perseveres:

BBC NewsBBC News
Mars: Nasa's Perseverance rover sends stunning imagesBBC

https://www.bbc.com/news/in-pictures-56238018
03-23-2021, 05:07 PM
Henry J
About Venus:

I'd read that billions of years ago, Venus may have had moderate temperatures and oceans. I didn't see how that would work if it was in the same orbit it's in now. But one variable I hadn't been aware of is the size and location of those oceans - smaller fraction of the planet than Earth's, and in the polar regions, not in the tropics. Apparently, that way it puts less water vapor in the air than one gets with large tropical oceans.

But then, around 700 million years ago, major volcanic activity overloaded its atmosphere with CO2, too much for it to be reabsorbed into the ground in time. Oops.
04-09-2021, 10:05 PM
Henry J
Ingenuity to make its first flight Sun night/Mon morning. (Middle of night for me, though.)
04-10-2021, 04:04 PM
Henry J
Delayed. Now no earlier than Wednesday.
04-20-2021, 11:48 AM
Henry J
Early Mon morning: We have liftoff! Granted, its flight time was under 1 minute, but gotta start somewhere, huh?

https://www.nasa.gov/press-rel...istoric-first-flight