I have a case of insomnia (my wife goes in for surgery tomorrow, and I am 2400 miles away), so I felt like tackling this.

Best wished, no matter how "small" the surgery is.

Let us know how things go.

Quote from: baldusi on 06/24/2011 03:57 pmBest wished, no matter how "small" the surgery is.Quote from: clongton on 06/24/2011 10:10 amLet us know how things go.Everything was a success, no issues. Thank you both for your concern, it means a lot.As for my late night rocket science, I hope I adequately answered where Jensen went astray. High temperature is good, but so is low molecular weight, and it's a trade between the two.Incidentally, nuclear rockets are governed by the same equation. The nice thing with nuclear is not so much that you can have higher temperatures. Your materials limits mean that they are about the same chamber temp as a chemical rocket.Where nuclear pulls ahead is your molecular weight and temperature are decoupled. You can use pure hydrogen, which is how you get 1000s of Isp. That's for solid core, of course. If you're talking about more exotic nukes, you can bump up temp too (I'm a fan of the nuclear lightbulb concept, myself).

Glad to hear that.I too am a complete fan of the nuclear lightbulb. That's why I said "a process to create pure silica" over in the thread about what do we want to see developed. That material is completely transparent to the thermal energy of a nuclear reaction so whatever thermal energy is left over from dealing with the pure hydrogen just goes out thru the glass engine into space. The isp would climb into the tens or even hundreds of thousands of seconds, and the thrust would climb right along with it.

Quote from: clongton on 06/24/2011 08:13 pmGlad to hear that.I too am a complete fan of the nuclear lightbulb. That's why I said "a process to create pure silica" over in the thread about what do we want to see developed. That material is completely transparent to the thermal energy of a nuclear reaction so whatever thermal energy is left over from dealing with the pure hydrogen just goes out thru the glass engine into space. The isp would climb into the tens or even hundreds of thousands of seconds, and the thrust would climb right along with it.Indeed, I've also wondered about that design using synthetic diamond. If you're not familiar with the CVD process for creating diamond, it's interesting. You make a low pressure, low temp carbon gas, and allow it to deposit on a preexisting diamond. The upshot is the technology has the potential to create relatively large, relatively arbitrary shapes out of diamond. Aside from temp resistance (as long as it's not in an oxidizer...), diamond has phenomenal thermal conductivity.

I too am a complete fan of the nuclear lightbulb. That's why I said "a process to create pure silica" over in the thread about what do we want to see developed. That material is completely transparent to the thermal energy of a nuclear reaction so whatever thermal energy is left over from dealing with the pure hydrogen just goes out thru the glass engine into space. The isp would climb into the tens or even hundreds of thousands of seconds, and the thrust would climb right along with it.

I imagine that even with atmosphere, if a person were to jump at the right speed, in the right direction, they could get very impressive hang time until just the air resistance slowed them enough to fall to the floor.

Quote from: Sparky on 07/08/2011 03:41 amI imagine that even with atmosphere, if a person were to jump at the right speed, in the right direction, they could get very impressive hang time until just the air resistance slowed them enough to fall to the floor.In other words, orbital velocity inside the torus is just the v=omega x R. For the Stanford torus v=pi*1.6 km /60 sec = 94 meters/sec. I don't think jumping into orbit will be an Olympic event.

Quote from: lcs on 07/08/2011 04:08 amQuote from: Sparky on 07/08/2011 03:41 amI imagine that even with atmosphere, if a person were to jump at the right speed, in the right direction, they could get very impressive hang time until just the air resistance slowed them enough to fall to the floor.In other words, orbital velocity inside the torus is just the v=omega x R. For the Stanford torus v=pi*1.6 km /60 sec = 94 meters/sec. I don't think jumping into orbit will be an Olympic event. 94 m/s = about 210.7 mph. At that speed, air resistance will VERY QUICKLY cause you to begin rotating again with the torus, and get pushed to the "floor".

Quote from: STS-134 on 07/08/2011 04:16 amQuote from: lcs on 07/08/2011 04:08 amQuote from: Sparky on 07/08/2011 03:41 amI imagine that even with atmosphere, if a person were to jump at the right speed, in the right direction, they could get very impressive hang time until just the air resistance slowed them enough to fall to the floor.In other words, orbital velocity inside the torus is just the v=omega x R. For the Stanford torus v=pi*1.6 km /60 sec = 94 meters/sec. I don't think jumping into orbit will be an Olympic event. 94 m/s = about 210.7 mph. At that speed, air resistance will VERY QUICKLY cause you to begin rotating again with the torus, and get pushed to the "floor".In any case, the answer to neutrino's question is that even in a vacuum, if you were suspended in the middle of the torus and suddenly released you would fall to the floor, because you would be moving in a straight line at the velocity of the torus, while the torus floor rushed up to meet you as it curved away from your straight line trajectory.

Q1: Roughly, what is the maximum bonus factor one can expect from the Oberth effect when injecting into Low Mars orbit (or Sun-Mars Lagrange point) fully propulsively with high thrust chemical rockets?

Q2: Given a chemical, single-stage MTV with 11 km/sec nominal delta v, if staged from EML1 or EML2, could one get an effective 44 km/sec total delta v using the Oberth effect when slingshotting around Earth and then braking into Mars orbit?

Q3: When departing Mars, can one get a significant Oberth bonus if the ERV was staged at Mars's Sun-Mars L-point?

Quote from: Warren Platts on 07/25/2011 05:03 amQ1: Roughly, what is the maximum bonus factor one can expect from the Oberth effect when injecting into Low Mars orbit (or Sun-Mars Lagrange point) fully propulsively with high thrust chemical rockets?The maximum bonus factor is infinite, in the case of an infinitesmal delta-v at perigee compared to delta-v at apogee (or v_inf, in the case of a parabolic orbit). It's not a matter of a clean "bonus factor", because the multiplier goes down with higher delta-v.QuoteQ2: Given a chemical, single-stage MTV with 11 km/sec nominal delta v, if staged from EML1 or EML2, could one get an effective 44 km/sec total delta v using the Oberth effect when slingshotting around Earth and then braking into Mars orbit?No. Even if you start from a parabolic escape trajectory and perform an 11km/s burn at an Earth grazing perigee, the resulting v_inf is still only sqrt((v_esc+delta_v)^2 -v_esc^2) = sqrt((11.1+11)^2-11.1^2) = 19.11km/s. This is a "bonus factor" of only 19.11/11 = 1.73.The "bonus factor" is higher for smaller delta-v. For example, a delta-v of .45km/s gives a v_inf of 3.19km/s. This is a "bonus factor" of 3.19/.45 = 7.09.A way to calculate the effect geometrically is to use a right triangle. The base is escape velocity; the hypotenuse is escape velocity plus delta-v. The other side of the triangle is velocity at infinity. When delta-v is small compared to escape velocity, the "bonus factor" is high. When delta-v is large compared to escape velocity, the "bonus factor" is low.QuoteQ3: When departing Mars, can one get a significant Oberth bonus if the ERV was staged at Mars's Sun-Mars L-point?I think so, if you're willing to accept very long trip times (on the order of many years). However, it would be better to stage at a highly elliptical Mars orbit. This gives you all of the benefit without any of the wait time. Similarly, staging at a highly elliptical Earth orbit gives you less of a wait time than EML1 or EML2.