New Mars Forums

Your propellant table looks at ISP and density. No mention of thrust to weight. If you regard gravity drag as significant, your tables should also look at T/W.

So 2.4 km/s for potential energy and 2 km/s for gravity loss? Sounds like you're still trying to get a vertical velocity vector with magnitude around 5 km/s.

As I portray it? Recall that the first stage going straight up and coming back down to the same launch pad is your image.

You imagined this first stage making a 5.25 km/s vertical velocity vector which is added to a 7.9 km/s horizontal velocity vector to get 9.4 km/s hypotenuse for your total delta V budget.

I stuck with your image since it was familiar to you. I noted a vertical ascent incurs gravity loss.

A 9.8 m/s^2 vertical acceleration is killed by gravity. It gives you 0 km/s. But this acceleration still consumes propellant, so you have to include the vertical a * t lost to gravity in your delta V budget.

Your mistake is assuming the lost vertical a * t gives a vertical velocity vector that you can add to the horizontal velocity vector. Doesn't work when velocity vector has magnitude zero.

Gravity loss can be arbitrarily large. You can make it as big as you want by increasing payload mass thus reducing thrust to weight ratio.

If you do a slow vertical ascent over 612 seconds, gravity loss is 6 km/s. Does that mean you can turn sideways, do an 8 km/s horizontal burn, and claim the 10 km/s hypotenuse as your delta V budget? No. Your total delta V budget would be 14 km/s.

Actual ascent trajectories typically start vertical and turn horizontal over time. If your acceleration vector is alpha degrees from horizontal, cos(alpha)|a| is the magnitude of the horizontal component and sin(alpha)|a| is the magnitude of the vertical component. The magnitude of the net vertical component would be sin(alpha)|a| - g + (w^2 * r), where w is angular velocity in radians and r is distance from earth's center. g is GM/r^2, of course.

In this case, the vertical acceleration component lost to gravity also doesn't add to vertical velocity. Even with this more accurate and complicated flight path, your model is wrong.

Nasaspaceflight.com has numerous threads on related topics. If you use search strings like ramjets, scramjets, Skylon, you will find many discussions.

One such discussion is The airbreathing space launch thread.

You admit this mistake and then ignore the correct numbers.

Again, the difference between 8.1 and 7.9 km/s is 1.6 MJ/kg.

This is NOT the same as the potential energy difference between earth's surface and a 300 km altitude, 2.81 MJ/kg.

You're trying (unsuccessfully) to get the numbers to meet your expectations.

This is not the scientific method.

I find it incredibly arrogant that you characterize dismissal of your models as dismissing the scientific method.

Thank you for some interesting links, Spacenut.

As you know, Tsiolkovsky's rocket equation is very prominent on my radar screen. That is why lunar water is the resource I'm most excited about.

But a major obstacle is energy to crack water into the hydrogen and oxygen propellant. Given power sources of plausible mass it is hard to crack water at the rates an orbital propellant market would demand.

And aluminum is much worse. Here on earth we dissolve alumina in molten halogen salts and then split the oxygen from aluminum by electrolysis. An extremely energy intensive process. If limitations to GLOW and power sources with low specific power are headaches for cracking water, they're much worse for mining aluminum.

Mining iron, titanium and other metals are also energy intensive. They do have an oxygen byproduct, though.

So one of the things I hope for are power sources with lots of watts per kilogram. Not only would this make ISRU more plausible but it would improve the performance of ion engines.

If we did get enough power on the moon to mine aluminum, silicon and other minerals, we could start making solar panels from ISRU materials. Then the lunar power constraints would be slain. But this is a very ambitious project.

I like this. Some of the best metal ores in our solar system are asteroids that come from differentiated bodies. These have better metal ores than found in planetary crusts. And it's possible that some metallic meteorites lie in the basins of lunar craters.

But lunar platinum couldn't be viable unless we had more economical transport to and from the moon. Again, volatiles are a prerequisite.

A few things this article brings up are the severe temperature swings and lack of volatiles. Both are much less of an issue at the lunar poles. Does the lunar KREEP extend to the poles? I don't know.

One of the hidden costs is environmental harm that rare earth mining inflicts. Not an issue on the moon. One of the harmful by-products is thorium. Possibly a lunar energy source. Kirk Sorensen has been trumpeting energy from thorium.

If luna infrastructure had enough power to make propellant and power rail guns, transportation costs would be cut a great deal. Possibly this would enable export of rare earths. But this a long term goal.

That's something I don't know much about. If you run across any articles on lunar metals, I hope you'll share them.

To better simulate Mars' hospitable environment, it would be better to put them in Hawaii?

What they could easily access on Mars is mixture of dirt and ice, also known as permafrost. Lots of that in northern Siberia.

One way to convince me would be to demonstrate your optimism is plausible.

Things like the Mars simulated mission fall short.

Rather than live in a tin can for years, they should plonk some people and equipment of plausible mass in northern Siberia. From this single location a handful of people would mine all the minerals they need and then use them to manufacture bulldozers, growlights, wires for power transmission, airlocks, air filters, grow food, make clothes, air filters etc.

Not only should they build a Walden pond in this hostile location, but a Walden Pond that has the infrastructure to manufacture heavy equipment, plumbing, etc..

Until you can demonstrate this, your argument is furious handwaving.

Mars would export gold or platinum? Sorry, this business case doesn't close by a long shot. Your expense would probably exceed your revenue by three or four orders of magnitude.

So a small population could sit down on Mars and come up with multi-trillion dollar ideas?

If the potential Mars settlers could do this on Mars surface why don't they just simply do this while they're still here on earth? This would solve the problem of funding a Mars mission.

You continue to miss my point.

You're trying to assess various factors that add to the delta V for getting to orbit.
We've discussed 1) Air drag, 2) gravity loss, and 3) change of energy for a higher altitude orbit.

Adding .2 km/s to a 6378 km circular orbit would boost it's energy to that of a 6678 km radius circular orbit. This exercise of comparing two circular orbits is to show show something about 3).

Revisiting the horizontal launch track on an airless earth. In such a scenario payloads could be launched with virtually no gravity loss and no air drag loss.

Starting from velocity = 0, 7.9 km/s would suffice to put an object in a 6378 km radius low circular orbit.

Starting from velocity = 0, 8.1 km/s would suffice to put an object in a 6678 km radius low circular orbit.

The acceleration lost to gravity over time doesn't give you a vertical velocity vector whose foot you can place on the head of a horizontal vector to give you a 9.4 km/s hypotenuse. This wrong model is what gave you 5.25 km/s to get above the atmosphere.

(Googling...) You just showed me something new.

Here's a 3D printer for metals objects. Lays down a layer of stainless steel powder. Then a binding agent (doesn't specify what binding agent). Then lifted out of the powder, heated and cured infused with bronze.

So three feed stocks: stainless steel, binding agent, and bronze. The feedstocks still need to mined from diverse places.

It's rough. Minimum detail size 1 mm. Doesn't specify how strong it is.

A typical product at Home Depot is made of different materials: copper, aluminum, glass, plastic, silicon are common. Is there one 3D printer that can accomodate diverse feedstocks?

When I see a 3-D printer that can print out working spark plugs as well as staplers, I'll might regard it as a substitute for our extensive manufacturing infrastructure.

And the materials for the feedstocks would still need to be mined.

I'm guessing your mental image looks something like this:

But in reality you don't get the 9.4 length by adding a 5.25 up leg to a 7.8 sideways leg.

A vertical ascent is done to get above the troposphere as quickly as possible. Typically the vertical ascent takes around 3 minutes.

During vertical ascent, gravity accelerates it down 9.8 meters/second^2. I'll round that to 10 meters/second^2 to make calcs easier.

During 3 minutes of vertical ascent your gravity loss is 180 seconds * 10 meters/sec^2. Which is 1800 meters/sec or 1.8 km/s.

At the top of the vertical ascent rocket speed is usually around zero. When altitude is achieved, the rocket turns sideways for the major horizontal burn.

http://blogs.airspacemag.com/moon/2011/ … a-gas-man/