Author Topic: Aerocapture and the knowledge of the atmosphere on Mars.  (Read 1853 times)

Offline speedevil

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Lifting entry, or capture using the atmosphere of Mars (BFR especially, though other craft are planned to use hypersonic lift to steer) obviously requires a good knowledge of the state of the atmosphere.

If your density estimate is off by 20km, and you need to force your trajectory down or up to meet the planned one, that's going to at best need lots of extra margin, may make you miss your target, and at worst lead to loss of mission.

There have 'recently' been a fair number of satellites around Mars concentrating on the properties of the atmosphere.

Is anyone aware of any published work on how knowledge of the atmosphere has changed, and perhaps more relevantly to near term plans, if different satellites, or more of them, or other measures would improve things?

« Last Edit: 02/20/2018 01:23 AM by speedevil »

Offline Russel

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Re: Aerocapture and the knowledge of the atmosphere on Mars.
« Reply #1 on: 04/03/2018 07:42 AM »
I would love to know this too. Incidentally there has been testing of air breathing ion engines to allow long lived very low orbit satellites on Earth. I'm wondering if this is applicable to Mars.

Using the upper atmosphere as fuel can mean lower mass and make it easier to have a largeish onstellation with good coverage.

Multifunction satellites (GPS included) which would give direct, accurate and real time data on the upper atmosphere.

Online A_M_Swallow

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Re: Aerocapture and the knowledge of the atmosphere on Mars.
« Reply #2 on: 04/03/2018 11:48 AM »
I would love to know this too. Incidentally there has been testing of air breathing ion engines to allow long lived very low orbit satellites on Earth. I'm wondering if this is applicable to Mars.

Using the upper atmosphere as fuel can mean lower mass and make it easier to have a largeish onstellation with good coverage.

Multifunction satellites (GPS included) which would give direct, accurate and real time data on the upper atmosphere.

Ion thrusters can be modified to use Argon as a propellant. Argon is 1.93% of Mars's atmosphere and is the main waste product from the CO2 extraction system.

Offline Russel

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Re: Aerocapture and the knowledge of the atmosphere on Mars.
« Reply #3 on: 04/05/2018 01:47 AM »
The idea was a constellation of very low Mars orbit satellites that rely on the Mars upper atmosphere for fuel. Rather than fuel being resupplied.

The reason I brought it up was that such satellites would be in the perfect location to do real time and accurate analysis of the Mars upper atmosphere. Very handy for aerocapture.

Offline speedevil

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Re: Aerocapture and the knowledge of the atmosphere on Mars.
« Reply #4 on: 04/10/2018 07:19 AM »

ftp://ccar.colorado.edu/pub/forbes/ASEN5335/DragReentry/28.AerobrakingAerocapture/28.%20Aerobraking%20&%20Aerocapture.pdf

Daily variations of the density of the atmosphere at 80km can be as high as twofold, with even higher variations on longer periods.
« Last Edit: 04/10/2018 07:21 AM by speedevil »

Offline Russel

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Re: Aerocapture and the knowledge of the atmosphere on Mars.
« Reply #5 on: 04/11/2018 01:11 AM »
You're definitely going to need realtime global data.

Offline john smith 19

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Re: Aerocapture and the knowledge of the atmosphere on Mars.
« Reply #6 on: 04/11/2018 01:12 PM »
You're definitely going to need realtime global data.
That's not entirely clear.

You should definitely have an Air Data System that can operate from orbit, rather than the flip out Pitot tubes on Shuttle. IIRC By the time they were giving reliable readings (around M3) about 95% of the Shuttles KE was already gone. FADS were baselined fro X38 and I think the X37b uses one.  I'm not sure how much atmospheric data is fed to it before it reenters and I doubt the USAF are going to say.

But I don't think there's any doubt if SX can make aerocapture (without propellant) work they can radically speed up the transit velocity, and hence cut the travel time. 
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

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