HopDavid
• Member for 7 years, 10 months
• Last seen more than a week ago
• Ajo, AZ

Assuming acceleration is constant, $d=(1/2) a t^2$. So plotted over time, distance traveled is a nice parabola. If you want the time it'd take for a specific distance, it's easy to manipulate $d=(1/... View answer Accepted answer 41 votes First a few terms: Low Earth Orbit (LEO) All spacecraft must first achieve low Earth orbit. This is true whether you're sending stuff to the Moon or Mars. Trans Mars Insertion (TMI) The burn needed ... View answer 24 votes After being released from an elevator, the payload and earth are a 2-body system. The paths in 2 body systems are conic sections: ellipses, parabola, and hyperbolas. What sort of conic section depends ... View answer 23 votes Edit Jan. 25, 2015: Geoffcc recently provided a link to words straight from the Horse's mouth, Elon Musk. Musk says the payload hit for RTLS (Return To Launch Site) is 30% vs a 15% payload hit for ... View answer Accepted answer 23 votes The speed of the probe doesn't change with regard to the assisting body. It is direction that is changed. If a hyperbolic orbit about the sun comes in with a Vinfinity of 5 km/s, it will exit with a ... View answer Accepted answer 22 votes Edit as of August 31, 2015: Looks like 2014 MU69 will be the post Pluto target. Paul Gilster has a nice article on Centauri Dreams. Edit as of Jan. 3, 2015: This article says 3 potential candidates ... View answer 21 votes Hohmann launch windows occur each synodic period. Or a more general version of a Hohmann transfer would be a transfer orbit tangent to both departure and destination orbits. This also occurs each ... View answer Accepted answer 21 votes In this pic the angle$\phi$is asin(6378/6878) or about 68º. It stays in the shade over 2 * 68º or about 136º. That's about 38% of the period. That's 2145 seconds or about 36 minutes. This is what ... View answer Accepted answer 18 votes Here's a pic of the tether proposed by Liftport. Go 160,000 km beyond EML1 and drop a payload from that point. It will follow an elliptical path whose perigee grazes low earth orbit. A 3 km/s burn at ... View answer 16 votes Hefty gravity wells can give a healthy Oberth benefit. Doing a burn deep in Neptune's well makes sense. Suggesting an Oberth maneuver near a Pluto sized object is pretty silly. Don't know if Randall ... View answer 15 votes If it is more dangerous, how much more and in what ways? Proffesorfish and Eli Skolas have both given thoughtful answers comparing the hazards of I.S.S. vs Moonbase. If humans were preceded by robots ... View answer 15 votes Kinetic energy is 1/2 mv2. Here's my visualization: When you add to that velocity v, you get a bigger square: Here Vb is velocity imparted by your burn. So for example, if you accelerate a kilogram ... View answer 14 votes I've been wondering this for years, not knowing how to approach the problem. Then at a NasaSpaceFlight thread a poster who calls him(her?)self R7 told me about dynamic pressure, also known as q.$q=....

Earth Carbon nanotubes might endure the enormous stress of an earth elevator but only short lengths have been manufactured so far. It would be a mega engineering project that would dwarf earlier ...

The major burn is a 7.7 km/s acceleration in the horizontal direction. But the first part of the trip is usually a vertical climb: Apollo Ascent profile from a NASA history page. Rescaled to show how ...

Here Robert Zubrin and Christopher McKay talk about terraforming Mars. Have your browser find "Moving Ammonia Asteroids" and it will take you to the relevant section about 3/4 down the page. Zubrin ...

What they teach in high school physics is wrong. When you toss a penny, it does not follow a parabolic path. Here is a picture of the penny's actual path (neglecting friction from air and rock and ...

One scheme for building elevators is to start from an anchor mass in synchronous orbit and to extend tethers down and up. The tether above will pull the anchor mass up and the tether below would pull ...

Gravity does not cancel out at any of the Lagrange points, not even L1. As you point out, at L2 both the central body and orbiting body are pulling the same direction. But there is a third character ...

To my knowledge there has been very little done in the 21st century. Here is a subsection of a page on space elevators and orbital tethers that lists tethers missions. The last two paragraphs are ...

Mass fraction and Tsiolkovsky's rocket equation make for major hurdles. Mf, or the ratio of propellent to dry mass is given by: $Mf=1-e^{-delta V/V_{exhaust}}$ To climb out of a steep gravity well ...

A Clarke style space elevator is a (very large) gravity gradient stabilized vertical tether. When in a rotating frame (as on a merry-go-round) you feel a tug. It's just inertia but feels like an ...

Two big ifs here. IF we achieved viable commercial fusion power (other than the sun) and IF Helium-3 was an indispensable part of this process. But for the sake of argument, let's say Helium-3 is the ...

I whomped up a spreadsheet to compare scenarios like this: Hohmann.xls. Typing Earth into departure planet cell and Mars into destination planet I get Launch windows open each 2.14 years (synodic ...

Using my Hohmann spreadsheet you can get an idea of approximate delta V and trip times. The spreadsheet assumes circular, coplanar orbits. So it's ballpark, not exact estimates. LEO to Mars capture: ...

Thanks for linking to my pdf! I have always assumed bi-tangential transfers took the least delta V. But your question has made me realize my assumption is conjecture. My goal is to find a general ...

You are talking about an elliptical orbit about the earth. Two points on this ellipse are of interest. Perigee - point on the orbit closest to earth. Apogee - point on the orbit farthest from earth ...

There were some major flaws in the backstory. I believe these were the movie studio's fault and not Andy Weir. In Tyson's trailer for the Martian The Hermes is harbored in low earth orbit between ...