New Mars Forums

Active plate tectonics probably stopped 3 billion years ago.  However, it's possible that there's still some seismic activity coming from residual geological activity such as active geothermal vents.  However, I can pretty much guarantee that Mars is pretty boring from a seismology perspective. 

The only possible use I can think of is to try and use seismology to locate geothermal hot spots of use for extracting water and generating energy for a Mars Base.  Also, geothermal vents are the best places to look for Martian life.

My understanding of the matter is that mass is a property completely independent up energy and matter.  Energy also has a mass - light is capable of bending spacetime because of its relativistic mass - although the effect is very small. 

E=mc^2 is a bit misleading as it implies that mass is only on one side of the equation.  In actuality, what it means is that the mass of the energy released when matter is converted to energy is the same as the mass of the matter.

So, the equation is actually:
m = m

However, we usually measure energy in units like Joules or ergs so the equation is written down as e=mc^2.  This merely is a conversion factor that converts mass units of energy into more standard energy units.

For example, one could write the equation as:
E = (1000*n/(6.022^23*FW))c^2
Where n = the number of atoms being converted to energy
and FW is the average atomic weight of those atoms.

To summarize:

Matter has a rest mass. 
Light/energy has no rest mass but does have a relativistic mass that represents the energy it carries.  If it had a rest mass, it would have infininte mass at light speed.

Yes, this is a well established fact - what's your point?

Well, here's a laundry list:

Problems with the maglev:

1: unless you get a large delta V from the maglev, it really gives a minimal improvement in the launcher performance.  The Saturn V 1st stage got the rocket to 200,000 feet and mach 5.  The relative amout of fuel and energy spent getting past the launch gantry were fairly minimal.  At most, you could reduce the launch mass of a 1st stage by maybe 20-30% with a subsonic launch platform.   You also have to add lots of weight for a rocket that is structurally capable of handling the stresses of accelerating both on a rail car and under its own power.   

2: The reduction in cost by using a slow maglev is going to be negative.   Less than 5% of the cost of a rocket launch is in the fuel.  Most of the cost is in personnel and facilities maintainance.  Using 10% less overall fuel and then adding the cost of designing, building and maintaining a maglev will result in a massive *increase* in your launch costs overall.

3: You add a whole new failure element in your launcher system.  You maglev is in a very hostile environment of avalanches and rockfall as well as horrendous thermal variations.  The rock on high mountain slopes is notoriously unstable because of freeze thaw cycles chewing it up.

Unless you can get a LARGE seperation speed with your maglev launcher, you actually make the launch more expensive.  By my very rough guesstimate, it needs to be something like mach 4 - perhaps as low as mach 3.   This also requires some sort of NASP type hypersonic air-breathing plane to take advantage of the large horizontal velocity.

Problems with retrobraking reentry:

1: your retro braking reentry requires an *absurd* amount of fuel.  In order to skip the whole aerobraking step, you have to lose ALL of your horizontal momentum and then lower yourself back down through Earth's gravity well.  This takes the same amount of energy as getting up into orbit.  To illustrate, imagine an Apollo comand capsule in LEO.  It would take a SATURN V attached to the back of it to do the retroreentry you are talking about.  To get  it to orbit, you would need a booster capable of lunching an entire fueled Saturn V to orbit.  An SSTO is barely possible as it is - it's patently impossible if you try your braking scheme.

In contrast, standard aerobraking reentry is relatively safe (one failure in the history of manned spaceflight) and very cheap if done correctly.  Correctly means forgetting the reusable reentry tiles and just using cheap ablative tiles.  You don't have to worry about extensive inspections or refurbishing - you just pull off the old tiles and slap on some new ones.  The Chinese are using resin treated wood as an ablative reentry shield. Heck the Apollo capsules used the equivalent of bathroom caulk for a reentry shield.  Spaceflight materials don't get much cheaper than THAT.

2: As GCNRevenger pointed out, you have an enormous safety issue - a single engine failure dooms the spacecraft to burning up or making a crater without a viable rescue or escape route.

I know that biotech these days is doing research on muscle growth and maintainance for people who have been rendered invalid because of hospitalizaiton.  I wouldn't be suprized that in 10 years we've got experimental drugs that can prevent or reverse much of the negative actions of 0-G

That might work - I'm not sure if the laser altimeter is designed to be able to do that sort of measurement, though.  At the least, it would require a dedicated instrument and then you also have the problem of trying to keep a laser focussed on a small target from a moving platform.  It's nothing that's insurmountable from an engineering point of view, though.  The biggest problem that I can see is that you only get short term monitoring of any given area.  To do good seismology, you need monitoring stations that can give 24/7 data.  The orbiter data would be 24/7 but split over a number of different observation sites.  On the other hand, this sort of data could still be useful and it's a lot cheaper to drop a bunch of tiny reflectors with some ablative shielding from orbit that it is to soft land a bunch of seismograph packages.

It would depend on the television model but I'm guessing no.  A television screen is designed to have a curvature that gets as flat of a screen as possible while still being able to withstand atmospheric pressure.  That curvature is probably not going to be the correct one for properly focussing light.  I suppose you could get lucky and have a Tv screen that would work but I think that it's unlikely.

Also, if you do try it, be careful - the inside of the TV tube is a vacuum and if you aren't careful, the tube can implode, spraying the area around it with high speed glass fragments.  Also, the glass has a high lead content and often the phosphors on the inside of the tube are toxic/carcinogenic.

Bringing the maglev speed back to mach 0.9 again puts the whole system back into the whole 'not worth it' regime.  The biggest advantage to this system is with an air breathing engine.  That would mean a ram/scramjet which needs supersonic speeds to operate.  I'd say that if the system can't get the spacecraft up to at least mach 2, it's not worth bothering with. 

What I've got envisioned is a NASP-type scramjet launcher that would come in a large and small variety for cargo and crew carrying respectively.  Truly massive cargo would probably still be launched on standard boosters but the ability to loft satellites and routine resupply missions will be essential if we want to maintain any sort of significant presence in space.

I'd also avoid retrograde braking since it will require your spacecraft to carry twice as much fuel.  The atmospheric reentry is actually a great boon - it lets you avoid having to pay for the massive delta V of getting back to the surface of th Earth without making a big crater.  I suspect that a craft with enough fuel to both take off and then land solely with retros will be vastly too heavy to even take off.

Actually, Apollo got shut down by Richard Nixon to help cover the cost of the Vietnam War but that's rather incidental.  Bush's interest in space is one of the few things I like about his presidency but I'll take what I can get.

The idea of using landfills is not bad - it's kind of like a proposal that the Brazilian(?) version of the Mars Society is developing right now.  They're working on developing autonomous greenhouses that could be set up by the millions all over Mars.  Basically, you've got a smalll bubble greenhouse that is kept warm by the greenhouse effect (suprise).  Inside, you've got plants and microbes converting the Martian atmosphere into something more palatable.  Evey once in awhile, you let the interior and exterior air mix to bring in more CO2 and to let out the O2, CH4 and other stuff that been made in the meantime.  It turns out that this approach, if feasible, would actually be much cheaper and faster than things like orbital mirrors.

I think that successful terraforming of Mars is going to require the use of every bright idea we can think of - landfills, greenshouses, orbital mirrors, etc.

BTW, you are correct about the technical reasons for Biospheres 2's failure.  However, I think that there's a deeper underlying reason for the failure.  For one, it was a poorly designed project from the start - trying to fit an ocean, jungle and grassland into the same greenhouse was just stupid.  Also, the thinking behind Biosphere 2 is similar to pre-Zubrin in-situ resource utilization.  Basically Biosphere 2 required that everything be self-contained.  This really isn't a viable option then dealing with something that small.  If Biosphere 2 had been allowed to occasionally bring in outside atmospheric gasses, etc, it would have done much better.

On MArs, we'll have the capability to generate huge quantities of O2 from the native atmosphere.  The nuclear reactors Zubrin uses for Mars Direct give quite a bit of lattitude in being able to manually tweak the environment.  Although terraforming MArs won't be simple, it wil be easier than Biosphere 2 was.

Having the probe resurface is a good idea.  All you'd have to do is have a big tank that you fill with ballast.  When you want to resurface, dump the ballast and refill the tank with air or vacuum.  The proble will then head back up.  However, I think that the probe's return will be much slower than its descent because you can't get all that much lift from buoyancy compared to the descent rate from dense ballast.

I'm not too sure about having a rover rendezvous with the emerged probe, though.  I don't know what Europa looks like from a rover's point of view but the sattelite images make it look pretty rugged.  Unless your probe resurfaced pretty close, I'd be afraid that it would hav a big canyon or something in the way.  Of course, if you have a tether, you can just follow the tether back up to the surface.

The submarine communications they refer to are ELF - Extremely Low Frequency radio communication that can punch through lots of water.  If you remember the movie Crimson Tide, the sub gets the partial message at the beginning from an ELF transmission.  However, if you remember, the message came in the form of a telegram.  ELF has such low data transmission rates because of the slow wavelength - it's not good for much more than Morse code.  I also wonder if it can punch through 20 km of solid ice.  I know very little about the technical side of ELF so I don't know what the answer to that is.

Of course, it would be better to try and find a thinner section of the ice for the probe such as a 'freckle' or one of those big rift faults.  The transit times will go down and your ability to communicate goes way up as the ice gets thinner.

As for mobility, when the probe breaks through the bottom of the ice, it can just leave behind a base station that's attached to the communication tether.  Some sort of robotic sub can then tool around, checking stuff out and occasionally head back to base to upload the latest data for transmission to the surface.

What would probably be best is some sort of tether that can carry information rich data like pictures.  An ELF transmitter on the sub would then act as a backup transmitter and a way to transmit smaller data chunks like temperature and chemical composition without having to return to the base station.

Curses!  You're correct, I had the thrust right but was underestimating the energy flux by several orders of magnitude.  It's pretty amazing that it takes a 100 MW of power output to keep a 100 m^2 area at 2200K. 

However, I think that it's not too implausible to have a small reactor with that power output.  Remember, we're not trying to pull electricity out of the core or control it very much.  Basically, we want some sort of short lived, very high energy nuclei that can be counted to decay at a very high rate.  Obviously, high power fluxes are possible - as nuclear weapons demonstrate.  Is it possible to get a mix of transuranics that can get a 100 MW/second thermal output?  Basically it's the mother of all RTG's.

Of course, the problem is that even if such a power flux is possible, you burn through your fissionables quite quickly.  Assuming that a 50 kg fissionable core can release 0.05% of it's mass as energy, you can run the engine for only about 6 months before the core runs out.  If it were 50 kg of antimatter, you could run the core for 500 years.  However, that's unlikely to happen. 

I'll need to run through the numbers again but it looks like the fuel fraction just jumped a few orders of magnitude.  It also looks as if this is now in the same ballpark as Zubrin's salt water nuclear rocket - just with a slightly better cargo mass fraction.  I'll see how the numbers turn out.

OK, I've been running some numbers on this nuclear photonic drive and... WOW, it's amazing.

I found some evaporation rates for Tungsten in vacuum at various temperatures and used it to find out what's a practical temperature to run the drive at. 

Assume a 100 kg total probe mass.  The drive is a small critical mass with a half life on the order of a century although we can moderate the system to try and get a steady level of output for a century, depleting the fuel in the process.  The critical core is contained in a spikey, polished and shiny tungsten jacket.  The spikes are to mazimize the surface area so that more light is emitted.  The jacket has a total surface area of 100 m^2.  I think that it's practical to have this whole package weight less than 50 kg.  The critical core is controlled to keep the outer surface of the jacket at 2200 K.  At this temperature, the evaporation rate is approximately 7*10^-6mg/cm^2 per hour.  Assuming our jacket geometry can withstand the loss of 10 mg of material per square centimeter(10 grams of material over the whole jacket), we're looking at about 160 years of active life. 

At that temperature, the total photon thrust (assuming perfect mirrors, etc) is about 0.59 N.  Assuming that we'll lose some of that thrust as randomly emitted IR re-emitted from imperfect mirrors, let's assume 0.5 N thrust.  This gives our 100 kg craft an acceleration of 0.005 m/s^2.

For about 100 years.

Here's a rundown of how our spacecraft does:
1 second: 0.005 m/s, 2.5 mm travel distance.
1 minute: 0.3 m/s, 9 meters travelled.
1 hour: 18 m/s, 32.4 km travelled
1 day: 432 m/s, 18,662.4 km travelled
1 year: 157.5 km/s, 16.5 AU travelled
10 years: 1580 km/s, 1664 AU travelled
100 years: 5.3% c, 2.63 LY travelled

Assuming an matter to energy efficiency of ~0.1%, I calculate that the craft will deplete 13-18kg of radioactives.  I'm assuming that this will require multiple core changeouts or some sort of liquid fission core that can be replenished.

If we take our nuclear 'bulb' and split it up into smaller bulbs, we can probaly get another 10-fold increase in surface area.  This would require 28 or so bulbs and gives an increase in the thrust to 5 N.  If the total mass remains the same, and we assume the same amount of fissible material, we deplete our drive in 10 years since we're now burning the cores 10 times faster to keep the same surface temperature on the jackets.  Therefore, now we achieve 5.3%c in 10 years instead but can no longer accelerate after that. 
1 year: 1574 km/s, 165  AU
10 years: 5.3% c, .26 LY
100 years: 5.3% c, 5.0 LY

If we start adding more fission fuel, the spacecraft gets heavier but can run the engine longer.  Assuming that the weight needed for replacement engine parts and fission fuel weighs about 50 kg/10 year burn, the maximum speeds of the probe increase with longer burn times as follows:
10 years: 5.3% c (100 kg probe)
30 years: 7.88% c (200 kg probe)
100 years: 9.5% c (450 kg probe)
200 years: 10.0% c (1050 kg probe)
1000 years: 10.4% c (10050 kg probe)

Obviously, the practical upper limit to the speed achievable by this system is about 9-10% light speed.  Not too bad for a glorified light bulb!