Atmospheric Grazing

Void · 2014-01-08 09:10:22

I wonder if the process of atmospheric grazing could support delivery of materials to Mars?

http://mars.jpl.nasa.gov/mro/news/index … NewsID=142

It has been done to help deliver automated missions to Mars already.

I guess I am thinking of an electric rocket system with solar panels. The objective would be to reduce the required propulsion mass for the delivery, by
using the solar panels as aerobraking devices after the electric rocket gets into Martian orbit. Grazing is a possiblity, and perhaps it could even be investigated if such solar panels could also serve as high altitude wings, but that makes it more complicated. I don't think active surfaces would work well at high altitudes such as flaps, but still it is an interesting thought.

The method if used could help to move payloads to low orbit. Perhaps consumables, fuel, and Oxydizers, or perhaps a lander.

Of course this would be in support of a following human mission to Mars.

It might also be involved in collecting samples from Phobos and Demos prior to achieving the low orbit.

Last edited by Void (2014-01-08 09:12:02)

RobertDyck · 2014-01-08 10:08:14

Aerobraking has been used for MGO, Odyssey, Mars Express, and MRO. MAVEN will dip into the atmosphere for samples; it isn't specifically "aerobraking", but will do that as part of its "dips". Mars Climate Orbiter tried to use aerocapture, but failed. It didn't fail due to any technology issue, it was a metric conversion error. The problem has been identified and corrected, sending another orbiter using aerocapture is long overdue.

Void · 2014-01-08 14:52:44

So could true aerocapture be used with a personed mission, and have a Ion Drive with grazing place some suppies in Mars orbit before it arrives?

RobertDyck · 2014-01-08 15:30:56

Sure. But aerocapture has to be successfully demonstrated with an unmanned probe before you commit human lives.

Void · 2014-01-08 17:33:29

I hear that and accept it as good thinking.

I am just thinking that some people want to get the crew down to the surface for radiation protection, so this would be a deviation, but I am thinking that with a supply ship grazed in to low orbit, and then a true Aerobraking crew capture, then might it take a few days to refit for landing with what the two ships had, then go down if all is good, from a low circular orbit. Less energy to shed with a heat shield on the lander.

I would wish that the heat shield from the crew insertion ship could be used in the landing, but I suppose it has to an ablation type heat shield, so would be used up.

I wonder if aerocapture experiments could be done with Earths atmosphere first. Get up into high Earth orbit, and then fire the engines on the experiment ship to direct the device to aerocapture into the Earths atmosphere at a high speed. That would then perhaps provide some understanding of how to do it with Mars? Or are they already confident that they know what they are doing?

Also there is a possible for an abort back to Earth, if all is not good with the equipment inventory.

Last edited by Void (2014-01-08 17:36:21)

RobertDyck · 2014-01-08 18:36:54

My idea is a bit different: maximum reuse. Over in Yet another Mars architecture I described a reusable ITV built at ISS. Transit from LEO to high Mars orbit, aerocapture and park. The idea of staying in a highly eliptical, high Mars orbit is one I got from a presentation at a Mars Society convention. The idea is barely in Mars orbit, so minimum energy to depart. I like it, so let's use it. Adding my ideas: use a parasol for a heat shield, made of the same fabric that NASA Ames used for their most advanced thermal blankets: DurAFRSI. That is Nextel 440. Make the ribs of titanium alloy for strength, light weight, flexible/bendable, and ability to endure high temperatures. This would not be enough to enter Mars atmosphere, but enough for aerocapture/aerobraking. I would do the opposite to what you proposed: drop all supply ships on Mars surface, park the crewed vessel in orbit. This provides a dedicated vessel for interplanetary transit. Click the link for further detail of my idea.

Ps. Some here had suggested an ion engine for supply ships. That's a great idea. I had included that at first, but forgot when I wrote the description in that thread. Ok, let's go back to that. Supply ships don't need to get there in 6 months, they could spend 2 years getting to Mars. Or perhaps an MPD thruster instead of ion, because MPD can use LH2 instead of xenon. Please keep that in mind when reading the link.

Last edited by RobertDyck (2014-01-09 13:57:39)

Void · 2014-01-08 19:00:11

Thats fine, I understand I am surely a lightweight in this area. I just wanted to get some answers. Nothing Marsshaking in what I presented, I will think about what you have replied with. I am still curious if aerobraking with the solar pannels of an ion rocket could earn their keep.

RobertDyck · 2014-01-08 19:27:03

As I said earlier, it's been done. Not with something big like a Mars hab, but with probes.

Void · 2014-01-09 06:54:29

I did have some arguments about eliptical vs low circular orbit.

True, for one architecture not involving a grazer, eliptical leaves a setup favorable to exiting the Martian orbit to go back to Earth.

However, if you have a highly efficient supply ship then getting out of the Martian gravity well is favored by resources made available at low circular orbit by the grazer.

I have been watching conversations about landers, and how hard it is to deal with the atmosphere of Mars during a landing. How hard it is to have a larger lander.

I would think that being in a lower energy orbit, a low circular orbit might make it just a bit easier, also getting back up the the orbital ship of course should be easier for a launch from the surface of Mars.

But I will see what you have to say.

Void · 2014-01-09 11:17:28

Perhaps both can happen. The people carrier in eliptical, the grazer in circular, with some taxi method for the people. But the taxi accumulates costs also. Maybe if the return to orbit craft was the taxi, and the landing craft was with the grazer?

But then you have to join the two in the circular orbit before landing on the surface. This would be a one use method for at least the lander stage.

RobertDyck · 2014-01-09 12:29:55

So your idea is to make entering the atmosphere with a large lander easier by slowing first. Use aerocapture to enter Mars orbit, and aerobraking to slow into lower orbit, before finally plunging into the atmosphere. A valid idea. Not sure if it's necessary. A specialist in atmospheric entry would have to comment.

My opinion is that direct entry is possible. One objective of Mars Science Laboratory (now called Curiosity Rover) was to prove NASA could land about one metric tonne on Mars. Curiosity is 899kg, so that's real close. It did enter via direct entry, no orbit. It was able to slow, use a parachute, and land. They didn't have to use the sky crane, that was a way to reduce total launch mass. They could have landed with a lander that has legs like Viking or Phoenix, landing rockets, a platform to hold the rover, and a ramp for the rover to drive down to the surface. But all that is heavy. They wanted it to fit on an Atlas V-541 launch vehicle. For an Atlas V the last 3 digits tell you the options they chose: '5' meter diameter payload fairing, '4' solid rocket boosters, and '1' engine for the upper stage. If they used a lander instead of sky crane, that would have been heavier, would have required a larger aeroshell (heat shield and back shell), and larger parachute. That would all be heavier, requiring a larger launch vehicle. It would probably have required an Atlas V Heavy, which has 3 core stages instead of 1 core stage plus small solid rocket boosters.

If you're going to land a large rover on Mars, for example a pressurized rover with life support the size of an RV, and no other habitat, they you would want the same sky crane as Curiosity. However, if you're going to land a habitat like Mars Direct they you won't have the wheels or suspension of a rover, so you'll need landing legs. Since you need legs anyway, just land the same way as Viking or Phoenix. The only real difference between that vs the Apollo Lunar Module is Apollo used a single landing rocket engine placed in the centre, while the Mars landers used several smaller engines placed on its sides. Apollo had 4 legs; the Mars landers had 3 legs forming a tripod. Mars landers had 3 engines, between the legs. Actually, I think Phoenix had a pair of smaller engines between each pair of legs, for a total of 6 engines. Smaller engines and spread out like that will kick up less Mars dirt when landing.

GW Johnson · 2014-01-09 12:49:40

Biggest problem with aerocapture/aerobraking schemes is the factor-2 variability of Mars atmospheric density profiles at high altitudes. Your design has to allow for this, so it is not as simple and lightweight as you might think at first. They had to allow for that with the probes that have used it, in the sense that the differences get partly made up at lower altitudes by lift during entry, and the rest "lost" in the uncertainties of chute deceleration.

Big items to be landed on Mars will not find chutes useful, as they penetrate to too low an altitude for a chute to deploy, much less do any deceleration good. That leaves retro-thrust rocket braking as the only practical terminal landing method.

I think for aerocapture, you will have to accept a factor-2 variable outcome, and carry the orbital maneuvering propellant to make up for it. For aerobraking, you will have to carry the extra propellant to make up the uncertainty in your retro-thrust rocket-braked terminal landing propellant.

Either way, you will be carrying extra propellants. Propellants that could do direct braking or orbit modification anyway. You won't save as much at Mars trying to use aerocapture/aerobraking as you would think at first glance. It is the density variability at high altitude that causes this dilemma.

Earth's atmosphere does not suffer this kind of variability at high altitudes, which is why we had no prior experience with it at Mars. It's why the landing ellipses were so very large on Mars, until very recently.

GW

Last edited by GW Johnson (2014-01-09 12:51:49)

RobertDyck · 2014-01-09 13:54:03

Mars Direct included a heat shield that was partially folded to fit within the fairing during launch, then unfolded for atmospheric entry at Mars.
71511-img2

Void · 2014-01-09 14:51:05

My part in this would be the atmosphere grazer to move materials to low orbit.

It was apparently considered worthwhile to move orbital probes this way, but the question would be if it could
also translate into useful resources delivered in an improved fashion in a landing event.

Aerocapture to orbit is an option for a ship delivered to an eliptical orbit. Other methods can deliver a
ship to an eliptical orbit.

So being told of the value of an eliptical orbit I have suggested a Taxi/Assent vehicle.

If a grazer were used perhaps it could have several landers, which would be left behind on the ground, and
the Taxi/Assent Vehicle might be used more than once.

But I might suggest that if a grazer were to have actuators on it's solar panels to change angles, then
a grazer might be able to compensate to a degree for variable atmosphric densities, to achieve the results
desired.

However I am not assured that an ion engine fired during the high part of the orbits can be enough to maintain
a safe or useful graze. That could be hoped, but when it gets to a more circular orbit it may require chemical
thrusters as well.

I am attracted to the notion of landing from a circular orbit, because I presume that more molecules of
atmosphere would be impacted before reaching the ground. A shallower entry angle. And of course the lander
would be moving at a lower speed during the beginning of entry, and perhaps further into it. I am presuming
that it might allow more liberty on the type of heat shield.

Last edited by Void (2014-01-09 17:35:53)

GW Johnson · 2014-01-09 17:03:41

For a given atmosphere, variables affecting entry gees, end-of-hypersonics altitude, and peak heating rates are (10 entry speed, (2) entry angle relative to horizontal, and (3) ballistic coefficient. Higher speed, steeper angle, and higher ballistic coefficient all act to increase gees and heating, and to decrease altitude, very sharply.

Entering from low circular orbit does two very beneficial things: (1) velocities are inherently low enough to eliminate the risk of "skipping off the atmosphere", and (2) entry angle is inherently very shallow, unless you are extremely wasteful in sizing your deorbit burn.

A pretty good sizing approach for the deorbit burn is the burn needed to take you into a surface-grazing ellipse. More is wasteful, much less might be ineffective.

Maneuvering around between high orbits low orbits, and elliptical orbits, costs propellant which must be dead-headed to Mars as payload for the outbound trip. In fact, it costs quite a bit, which is what my "Mars Mission Study 2013" posted over at "exrocketman" found.

The lowest circular orbit stable for the requisite time seems to be the best overall choice for missions that stage out of orbit, so as to make more than one landing in the one trip to Mars. That's probably somewhere near 300 km altitude on a 1-year time scale, maybe nearer 500 km on a multi-year time scale.

GW

Void · 2014-01-09 17:37:01

Thanks for the education.

Quaoar · 2014-01-10 15:38:42

GW Johnson wrote:

Biggest problem with aerocapture/aerobraking schemes is the factor-2 variability of Mars atmospheric density profiles at high altitudes. Your design has to allow for this, so it is not as simple and lightweight as you might think at first. They had to allow for that with the probes that have used it, in the sense that the differences get partly made up at lower altitudes by lift during entry, and the rest "lost" in the uncertainties of chute deceleration.
Big items to be landed on Mars will not find chutes useful, as they penetrate to too low an altitude for a chute to deploy, much less do any deceleration good. That leaves retro-thrust rocket braking as the only practical terminal landing method.
I think for aerocapture, you will have to accept a factor-2 variable outcome, and carry the orbital maneuvering propellant to make up for it. For aerobraking, you will have to carry the extra propellant to make up the uncertainty in your retro-thrust rocket-braked terminal landing propellant.
Either way, you will be carrying extra propellants. Propellants that could do direct braking or orbit modification anyway. You won't save as much at Mars trying to use aerocapture/aerobraking as you would think at first glance. It is the density variability at high altitude that causes this dilemma.
Earth's atmosphere does not suffer this kind of variability at high altitudes, which is why we had no prior experience with it at Mars. It's why the landing ellipses were so very large on Mars, until very recently.
GW

So the SpaceX choiche to use supersonic retropropulsion to slow down the Red Dragon capsule insetead of parachute is correct.

Tom Kalbfus · 2014-01-15 16:47:33

Void wrote:

I wonder if the process of atmospheric grazing could support delivery of materials to Mars?
http://mars.jpl.nasa.gov/mro/news/index … NewsID=142
It has been done to help deliver automated missions to Mars already.
I guess I am thinking of an electric rocket system with solar panels. The objective would be to reduce the required propulsion mass for the delivery, by
using the solar panels as aerobraking devices after the electric rocket gets into Martian orbit. Grazing is a possiblity, and perhaps it could even be investigated if such solar panels could also serve as high altitude wings, but that makes it more complicated. I don't think active surfaces would work well at high altitudes such as flaps, but still it is an interesting thought.
The method if used could help to move payloads to low orbit. Perhaps consumables, fuel, and Oxydizers, or perhaps a lander.
Of course this would be in support of a following human mission to Mars.
It might also be involved in collecting samples from Phobos and Demos prior to achieving the low orbit.

I also wonder how it could support deliver to Venus orbit? A given asteroid would have more opportunities to send material to Venus orbit than to either Mars or Earth through atmospheric grazing for a very simple reason: Venus' orbital period is 224.7 Earth days, Earth's is 365.24 days, and Mars is 686.78 Earth days. Lets take the asteroid Ceres as an example, it has an orbital period of 1,680.5 Earth days.

Here's how I'll do the math:
Venus has an orbital period of 224.7 days that is 360 degrees of its orbit is covered in this time. This translates to 360 degrees/224.7 days = 1.602 degrees/day.
Earth has an orbital period of 365.24 days, this translates to 360 degrees/365.24 days = 0.9857 degrees/day.
Mars has an orbital period of 686.78 days, this translates to 360 degrees/686.78 days = 0.5242 degrees/day.
Ceres has an orbital period of 1,680.5 days, this translates to 360 degrees/1,680.5 days = 0.2142 degrees/day.

I have to calculate how long it takes, approximately for each of these planets to reach the same position in its orbit relative to Ceres.
T(Venus)=1.602V degrees/day
T(Earth)=0.9857E degrees/day
T(Mars)=0.5242M degrees/day
U(Ceres)=0.2142C degrees/day

T(Venus)-U(Ceres) = 360
T(Venus)=360 + U(Ceres)
1.602V = 360 + U(Ceres)
1.602V = 360 + 0.2142C
C=V
1.602V = 360 + 0.2142V
1.3878V = 360
V = 360/1.3878 = 259.403 days Venus

T(Earth)-U(Ceres) = 360
T(Earth)=360 + U(Ceres)
0.9857E=360 + 0.2142C
C=E
0.7715E=360
E = 360/0.7715 = 466.623 days Earth

T(Mars)-U(Ceres) = 360
T(Mars)=360 + U(Ceres)
0.5242M=360 + 0.2142C
C=M
0.31M = 360
M = 360/0.31 = 1,161.290 days Mars

So lets compare them,
If your going to receive material from the asteroid Ceres at Mars in a minimum energy transfer orbit, you can do so every 1,161,290 days (3.179 years)
If your going to receive material from the asteroid Ceres at Earth in a minimum energy transfer orbit, you can do so every 466.623 days (1.278 years)
If your going to receive material from the asteroid Ceres at Venus in a minimum energy transfer orbit, you can do so every 259.403 days (0.710 years)

Time is money in economics, so the most economical place in the Solar System to receive asteroid materials is the planet Venus, as it is the innermost planet with a substantial atmosphere. Asteroid mined from Ceres can be sent toward Venus every 0.710 years when there is an optimal alignment between the planet Venus and Ceres. This would make the space around Venus an excellent manufacturing hub and the availability of Solar Energy is twice that of the space around Earth, and Solar collectors would need only about half the area as they would around Earth to gather the same amount of energy for industrial activities. I think Venus would prove an excellent manufacturing base for a Solar System wide economy, so the nation or companies that get first dibs on the space around Venus are going to have an excellent economic advantage over any place else in the Solar System.

Last edited by Tom Kalbfus (2014-01-15 20:50:30)

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#1 2014-01-08 09:10:22

Atmospheric Grazing

#2 2014-01-08 10:08:14

Re: Atmospheric Grazing

#3 2014-01-08 14:52:44

Re: Atmospheric Grazing

#4 2014-01-08 15:30:56

Re: Atmospheric Grazing

#5 2014-01-08 17:33:29

Re: Atmospheric Grazing

#6 2014-01-08 18:36:54

Re: Atmospheric Grazing

#7 2014-01-08 19:00:11

Re: Atmospheric Grazing

#8 2014-01-08 19:27:03

Re: Atmospheric Grazing

#9 2014-01-09 06:54:29

Re: Atmospheric Grazing

#10 2014-01-09 11:17:28

Re: Atmospheric Grazing

#11 2014-01-09 12:29:55

Re: Atmospheric Grazing

#12 2014-01-09 12:49:40

Re: Atmospheric Grazing

#13 2014-01-09 13:54:03

Re: Atmospheric Grazing

#14 2014-01-09 14:51:05

Re: Atmospheric Grazing

#15 2014-01-09 17:03:41

Re: Atmospheric Grazing

#16 2014-01-09 17:37:01

Re: Atmospheric Grazing

#17 2014-01-10 15:38:42

Re: Atmospheric Grazing

#18 2014-01-15 16:47:33

Re: Atmospheric Grazing

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