NASA’s Balance Mass Challenge

[TythosEternal]

NASA's Balance Mass Challenge: Using “Dead Weight†on Mars Spacecraft to Advance Science and Technology

Official press release: http://www.nasa.gov/solve/marsbalancechallenge/#.VCD09PldV8E

ADHD version:

This is a proposal paper outlining a mission plan. It does not involve the construction of actual hardware. There is a monetary award for the winning team.

I have two separate motions, if you will:

• I propose we put together a KSP InnoCentive team (I have already registered, but not yet submitted a solution). This team will be responsible for submitting a written proposal for this challenge. I will organize the team and act as the interim manager until a formal organizational structure can be put into place. If you are interested, please send an email to [email protected] with a description of the functional role you'd like to play and the specific contributions you will be able to make to the project.
  
• While the team will be responsible for converging on the final concept, it's only appropriate to open up the brainstorming to everyone in our community! Given previous discussions, I would suggest we start with the following ideas:
  
  • Phobos orbiter/lander/impactor
    
  • High-altitude spectroscopy (i.e., complement the MAVEN and MOM mission discoveries by mapping specific distributions)
    
  • Infrared mapping (single-instrument MGS follow-on)
    

Let the goings-on begin!

[Tommygun]

Some kind of seismic reflection experiment could be used for the six 25kg Entry Mass Balance Devices.

[shynung]

I'm thinking of tungsten harpoons with sensors at the tip, to look for moisture (and probably more) beneath the surface. Here's hoping it wouldn't simply bounce off a boulder.

[DerpenWolf]

I was wondering when a thread on this would pop up! I'd personally like to drop a high velocity tungsten slug and make a hole. Then maybe on of the older rovers ( assuming you impacted this relatively close) could take a look inside (or maybe something from one of the other balance masses!). I kind of doubt they would do this but if they did it would be interesting. Also do you think we could make a bare-bones landing system with that much mass? It would be very cool if we could get a kilogram or two to the surface!

[Rakaydos]

I wonder if you can fly a blimp of sensors using 75kg of matierial.

[Tommygun]

Don't the two 75kg loads normally stay in orbit?

[Rakaydos]

Don't the two 75kg loads normally stay in orbit?

I believe the phrase was "Prior to atmospheric entry."

[Guest]

Just add expendable batteries.

[magnemoe]

Why do they drop ballast? to change center of mass? might be posible to do another way like moving the cargo inside the heat shield?

[cakepie]

I'd personally like to drop a high velocity tungsten slug and make a hole. Then maybe on of the older rovers ( assuming you impacted this relatively close) could take a look inside (or maybe something from one of the other balance masses!).

More likely the rover that needed these very balance masses, or, as you suggest, a mini rover of sorts from another balance mass. I don't think they'd land a new rover that close to the old ones, much better value to be had exploring a new area.

Don't the two 75kg loads normally stay in orbit?

In the case of Curiosity, they impacted: http://www.nasa.gov/mission_pages/MRO/multimedia/pia16456.html

Why do they drop ballast? to change center of mass? might be posible to do another way like moving the cargo inside the heat shield?

Yes, with Curiosity, the 2x75kg are on one side of the entry capsule, and 6x25kg on the other side, initially balanced. They jettison the first pair to shift the CoM of the capsule, which acts as a lifting body, then the set of 6 are ejected at the end of guided entry phase to restore balance before parachute phase:

... The cruise balance masses (2), and the entry balance masses (6). The cruise balance masses are ejected after the entry capsule has been despun. They serve the purpose to generate a cg offset such that the capsule will have an L/D of .2 at mach 24. The entry balance masses are ejected right before the opening of the parachute to eliminate the cg offset. Six masses ejected over a period of few seconds enable a slow correction of the trim angle of attack

"Moving the cargo" around would have to introduce complexity in order to still ensure the payload (i.e. rover) is safely delivered to surface. You'd also need room in order to move things around. Much easier to just pack the payload securely in the capsule, and use small, dense ballast.

~ ~ ~

Since the numbers given are from MSL/Curosity, it's not unreasonable to assume that having gained confidence from the success of that landing, they're ready to try something more useful besides dumb ballast next time, i.e. Mars 2020 which will be based on the same rover design. Would be great to aim for something that would synergize with the rover's science payload.

I wonder if you can fly a blimp of sensors using 75kg of matierial.

I like this very much, exactly what I was thinking as well. A lot better than a drone that uses wings, in my opinion, because lifting surfaces means you'd need some sort of airstrip to land and take off. An electrically propelled blimp would be much more versatile in that it could go almost anywhere, and have a longer useable lifespan. It would also have the benefit of packing into a smaller volume.

Perhaps two blimps, using the first set of 2x 75kg masses, and some in-situ science experiment payloads in the 6x 25kg that could be picked up and (re)deployed by the blimps or the new rover.

I'm thinking that the blimps could be deployed in atmosphere by a combination of parachutes and change in bouyancy (inflation of envelope with compressed lifting gas). It might be possible for parachute to become envelope, saving some mass. Blimps will land after deployment for diagnostic checks. Subsequently they can be used to scout ahead for the rover, to help find features of interest that are worth a visit. They can also collect samples and deliver them back to the rover. Of course, also moving the 6x 25kg payloads as well as operating independently.

6x 25kg science payloads could be parachute+airbag landed. First ideas that come to mind (without thinking too hard):

- mini meteorological/environmental station with a similar suite of sensors as Curiosity REMS or Mars 2020 MEDA

- revive the mini-greenhouse idea of MPX, with the ability to deploy in different locations. Or other plant/algae/bacteria experiment.

- sample collection and caching

[Idobox]

I wonder if you can fly a blimp of sensors using 75kg of matierial.

I though it was not possible, the atmosphere of Mars being only 20g/m^3 at the surface, compared to 1.2kg on Earth, then I did math.

Let's imagine a hydrogen balloon on Mars. At 6mb and 210K (average temperature), hydrogen has mass of .7g/m^3, which gives more or less 19g/m^3 of lifting power.

This balloon http://www.scientificsonline.com/product/professional-weather-balloon is 600g for 6m diameter, which gives a material density of 5g/2

For 10m radius, we get 80kg of lifting force, for a mass of 6kg.

For 20m radius, we get 650kg lift, 25kg mass.

A balloon is completely feasible if you find a way to make it survive entry. I imagine a heatshield to bleed most of the velocity, and a small SRB to kill the rest before inflating the balloon at high altitude could work. Latex, which is the most common material for weather balloon might not be a good choice for a Mars balloon given the temperatures and radiation, but the CO2 atmosphere gives a surprising amount of lift and heavier materials could probably work.

[sgt_flyer]

One small problem with your hydrogen balloons - you'll need to have a way to store this hydrogen for the duration of the trip. (And hydrogen is not easily storable - with boiloff (if cryogenically stored) and leakage (hydrogen atoms are too small, and can pass through other materials - the thinner the easier)

The best way, would be to store stable chemicals that could create the desired amount of hydrogen when mixed (and once you have your hydrogen, dump (or use for something else) the byproducts of the reaction. (Of course, those chemicals would take a significant amount of your allocated weight)

Regarding reentry, if the balloon can be inflated in vaccuum without tearing, it might allow for sufficient drag to slow down in atmo with minimal heatshielding (as the inflated balloon would have an extremely low density - very high drag compared to it's mass)

Regarding the 75kg masses, i would say some microsats (maybe using DSSP electric SRBs which were sent in a microsat to ISS for testing - those would be ideal for allowing microsats to do orbital manoeuvers - (a microsat with ion propulsion might have difficulties having enough sunlight at these distances)

The balloons could eventually be tucked inside the 25kg masses - as those would be dropped after atmospheric entry, no need for protecting the balloons from reentry. Such Balloons could be useful with some kind of tracking system that orbiting satellites could detect - such as allowing better surveys of the wind speeds and directions.

Edited September 25, 2014 by sgt_flyer

[Idobox]

Still about balloons, NASA is working on it.

http://mars.jpl.nasa.gov/technology/balloons/

The material of the balloon appears to be the main issue, and they want to fill it with helium, for some reason (I assume because hydrogen leaks through pretty much anything, including balloons), and it would be limited by leaks.

An other interesting approach I though of: N2 and Argon are lifting gases on Mars, and there is 2.7 and 1.6% of them. At 210K, CO2 will freeze around 5 atm, but heat it a little bit, and you can liquefy it (triple point is 217K, 5.1 atm). At this kind of pressure and temperature, N2 and Ar are still gases, so extracting them is relatively easy, you just need to compress the atmosphere to 6 or 7 atm (comparable to car tires) at 230K, keep the gas part and purge the liquid. A simple pump and two electrovalves on top and bottom of the tank would suffice. Alternatively, membranes could be used at lower pressures.

Of course the resulting gas would be significantly heavier than H2 or He, but you would have a limitless supply of it. Molecular weight of N2 is 28g/mol, Ar is 40g/mol, at this ratio, you would get an average weight of 32.5 g/mol, compared to 43 for the atmosphere, the density would be 11.6g/m^3, and the lifting power around 8g/m^3 lifting power, less than half what you would get with H2 or He.

With pure N2 (not sure how to separate it from Argon, but they go supercritical at very different pressures, which might be a way), you would have 28g/mol, 10g/m^3 mass, and roughly 10g/m^3 of lifting power. Probably not worth separating N2 and Ar.

Another big point in favor of N2 is that it can easily be produced by heating a mixture of powders. Airbags use a very fast reaction between NaN3 and KNO3, but there are probably more mass efficient solutions.

Regarding reentry, if the balloon can be inflated in vaccuum without tearing, it might allow for sufficient drag to slow down in atmo with minimal heatshielding (as the inflated balloon would have an extremely low density - very high drag compared to it's mass)

Entry velocities for Mars probes goes from 4.5 to 7.5km/s. That's a lot of energy to shed. For 75kgs at 5.5km/s (MSL entry speed), it means about 1GJ. Spread equally over an arbitrary 10minutes, it still means a little less than 2MW of heat. Spread over 1h (because buoyancy keeps you at high altitudes), it is still represents 315kW. No balloon can survive that kind of heat, you're going to need a heatshield, like the inflatable ones NASA is working on.

[ximrm]

I suggest ejecting small models of Jeb made of pure gold.

[sgt_flyer]

Still about balloons, NASA is working on it.

http://mars.jpl.nasa.gov/technology/balloons/

The material of the balloon appears to be the main issue, and they want to fill it with helium, for some reason (I assume because hydrogen leaks through pretty much anything, including balloons), and it would be limited by leaks.

An other interesting approach I though of: N2 and Argon are lifting gases on Mars, and there is 2.7 and 1.6% of them. At 210K, CO2 will freeze around 5 atm, but heat it a little bit, and you can liquefy it (triple point is 217K, 5.1 atm). At this kind of pressure and temperature, N2 and Ar are still gases, so extracting them is relatively easy, you just need to compress the atmosphere to 6 or 7 atm (comparable to car tires) at 230K, keep the gas part and purge the liquid. A simple pump and two electrovalves on top and bottom of the tank would suffice. Alternatively, membranes could be used at lower pressures.

Of course the resulting gas would be significantly heavier than H2 or He, but you would have a limitless supply of it. Molecular weight of N2 is 28g/mol, Ar is 40g/mol, at this ratio, you would get an average weight of 32.5 g/mol, compared to 43 for the atmosphere, the density would be 11.6g/m^3, and the lifting power around 8g/m^3 lifting power, less than half what you would get with H2 or He.

With pure N2 (not sure how to separate it from Argon, but they go supercritical at very different pressures, which might be a way), you would have 28g/mol, 10g/m^3 mass, and roughly 10g/m^3 of lifting power. Probably not worth separating N2 and Ar.

Another big point in favor of N2 is that it can easily be produced by heating a mixture of powders. Airbags use a very fast reaction between NaN3 and KNO3, but there are probably more mass efficient solutions.

Entry velocities for Mars probes goes from 4.5 to 7.5km/s. That's a lot of energy to shed. For 75kgs at 5.5km/s (MSL entry speed), it means about 1GJ. Spread equally over an arbitrary 10minutes, it still means a little less than 2MW of heat. Spread over 1h (because buoyancy keeps you at high altitudes), it is still represents 315kW. No balloon can survive that kind of heat, you're going to need a heatshield, like the inflatable ones NASA is working on.

well, one main usage of helium in spacecraft is pressurisation of the fuel tanks as the spacecrafts no longer needs it's RCS system post reentry, they could use their pressurizing gases to fill up small balloons

regarding reentry of a balloon, remember that you would also have at your disposal a much larger surface for dissipating heat (that's why i mentionned minimal heatshielding) - 375kw spread over the full surface of the balloon, maybe we can use this surface to exchange more heat with the atmosphere too, limiting the necessary amount of shielding (maybe some thin layer of the new sprayable ablative shielding they are develloping could do the trick, so they don't weight down the balloon post reentry )

[Idobox]

well, one main usage of helium in spacecraft is pressurisation of the fuel tanks as the spacecrafts no longer needs it's RCS system post reentry, they could use their pressurizing gases to fill up small balloons

regarding reentry of a balloon, remember that you would also have at your disposal a much larger surface for dissipating heat (that's why i mentionned minimal heatshielding) - 375kw spread over the full surface of the balloon, maybe we can use this surface to exchange more heat with the atmosphere too, limiting the necessary amount of shielding (maybe some thin layer of the new sprayable ablative shielding they are develloping could do the trick, so they don't weight down the balloon post reentry )

10 minutes with a 10m radius balloon gets you around 1.5kW/m² if the heat is distributed uniformly on the sphere. 6kW/m² if you only consider the disk (as in, the back of the balloon stays cold). It won't survive.

1h with a 20m radius balloon, you get around 62 or 250W/m^2, much more survivable, but still difficult for a µm thin layer of polymers.

Also, the payload would be in the front, and would pull strongly on the balloon.

Heatshields are a mature technology, and the terminal velocity on Mars is reasonable. Here is a link to a NASA calculator.

http://exploration.grc.nasa.gov/education/rocket/termvr.html

For 75kg and a cross section of .5m², I found 288m/s. Pathfinder went from 7.3 to .4km/s in a little bit more than 3 minutes and only then opened its parachute at 11km altitude.

I would use an ablative heatshield to kill most of the velocity, and start inflating the balloon slowly to use it as a parachute, keeping the traction low until buoyancy cancels weight.

Actually, balloons are a very good way to land a rover. Terminal velocity with a parachute was around 60m/s for pathfinder, 76m/s for Curiosity (much higher altitude). A balloon could be inflated quite easily at that point.

I really wonder why they thought a rocket powered skycrane would be easier/safer (it is awesome, but I don't expect NASA to care much for awesomeness when they make that kind of decision).

[sgt_flyer]

10 minutes with a 10m radius balloon gets you around 1.5kW/m² if the heat is distributed uniformly on the sphere. 6kW/m² if you only consider the disk (as in, the back of the balloon stays cold). It won't survive.

1h with a 20m radius balloon, you get around 62 or 250W/m^2, much more survivable, but still difficult for a µm thin layer of polymers.

Also, the payload would be in the front, and would pull strongly on the balloon.

Heatshields are a mature technology, and the terminal velocity on Mars is reasonable. Here is a link to a NASA calculator.

http://exploration.grc.nasa.gov/education/rocket/termvr.html

For 75kg and a cross section of .5m², I found 288m/s. Pathfinder went from 7.3 to .4km/s in a little bit more than 3 minutes and only then opened its parachute at 11km altitude.

I would use an ablative heatshield to kill most of the velocity, and start inflating the balloon slowly to use it as a parachute, keeping the traction low until buoyancy cancels weight.

Actually, balloons are a very good way to land a rover. Terminal velocity with a parachute was around 60m/s for pathfinder, 76m/s for Curiosity (much higher altitude). A balloon could be inflated quite easily at that point.

I really wonder why they thought a rocket powered skycrane would be easier/safer (it is awesome, but I don't expect NASA to care much for awesomeness when they make that kind of decision).

Well idobox i was referring for minimal heatshielding at this kind of technology

http://www.google.com/patents/US4112179

You could spray coat a thin layer of it at the surface of your balloon with this kind of ablative material before launch, (the payload could still keep it's own shielding -ejecting 1.5kw of energy/m of energy through ablation should be pretty easy - and no need of a ejection mecanism (if it's less complex, it could become more reliable) - the ablation would be calculated to remove almost all of the ablative material diring reentry, keeping only the balloon. (The reentry heat could also further expand the balloon (if built for that) if we transfer some of this heat to the gases inside the balloon - decreasing even further density during reentry (could help counteracting the additional weight of an ablative coating)

[TheFlyingPigs]

I suggest ejecting small models of Jeb made of pure gold.

Genius! We could launch a Model rocket for him to sit on

[Error404brain]

For the ballons, what about CH4 or some other hydrocarbure ?

We then break the bond for to get the h and here we go.

otherwise, can't we also put something in orbit of mars ? (for to go to phobos )

You could spray coat a thin layer of it at the surface of your balloon with this kind of ablative material before launch, (the payload could still keep it's own shielding -ejecting 1.5kw of energy/m of energy through ablation should be pretty easy - and no need of a ejection mecanism (if it's less complex, it could become more reliable) - the ablation would be calculated to remove almost all of the ablative material diring reentry, keeping only the balloon. (The reentry heat could also further expand the balloon (if built for that) if we transfer some of this heat to the gases inside the balloon - decreasing even further density during reentry (could help counteracting the additional weight of an ablative coating)

=> we can't, the baloon will be already in overfill, he wouldn't resist that kind of thing.

[Rakaydos]

A solar powered self inflating Nitrogen balloon with a Radar target and an unspecified science payload (bonus points if we can make the radar target variable reflective and use it as a low power passive transmission method) in a 25kg mass sounds like a strong proposal. Making one with independant robotic steering (like the Tandem Airship) that can survive reentry as a 75 KG mass is also interesting, as it can actually rendivous with other rovers and give close air support. (put an anchor hook on it, for instance, to lift a -small- stuck rover)

[Maxwell Comp]

I think you guys are finding brilliantly exotic ideas, but there's a simple one we could try for the in-atmosphere ejection.

Because of Mar's low atmospheric density and lower mass, it requires much less power to reach escape velocity than from Earth. In fact, a small rocket could easily be made that could escape Mars's atmosphere, with mass and space to spare. According to Air & Space magazine, a rocket the size of a pencil could do it. That rocket can be fired upwards away from Mars and collect atmospheric samples on the way up.

The other 150kg of mass ejected earlier could be another rocket, and the two rockets could link and begin a return trip to Earth.

It's a relatively simple sample return mission. The hardest part would be the orbital docking, but the rockets will already be along aligned orbits. Preservation of the returned sample will be important because there will be very little martian dust/atmosphere in it, but there will be enough to experiment with.

[metaphor]

I think the payload also has to have a similar mass as the tungsten, or at least 90% of it. That means it needs to be dense, so would be a problem for blimps meant to be filled by a light gas (stored as a liquid).

[cakepie]

The mass certainly does need to be within the specified parameters, but I'm fairly sure there's a good bit of room to play with when it comes to volume, so I don't think it needs to be as dense. The NASA video references gliders and mini rovers; those are quite a bit bigger than ballast blocks.