Recent content by HopDavid

For ballpark Hohmann numbers you could use the spreadsheet I used to make my Cosmic Train Schedule page. Here's a screen capture for arrival to a Deimos orbit: You can see insertion to this orbit takes about a 2 km/s periapsis burn. Here's a capture orbit with Deimos at apoapsis A 1...

SpaceX just sent a payload to SEL1.

There is a Farquhar route from LEO to EML2 that takes about 9 days. It takes about 3.1 km/s to depart LEO then a .18 and a .15 km/s burn to get to EML2. The orbit's time reversible so about .33 to drop from EML2 to a near earth perigee. The ship would be moving just under escape at perigee...

Sorry about thread necromancy. But Venus cyclers have long been one of my favorite daydreams (see my animation of this scheme) My enthusiasm was dampened somewhat when I was looking at broken plane transfers. Venus' inclination is ~3.4º. So, unless the cycler rendezvous point coincides with an...

I believe a straight old fashioned Hohmann from LEO to EML2 would take about 4 km/s. Remember EML2 is moving faster than a ordinary orbit at that altitude, so even more delta V is needed to circularize at apogee. Farquhar's use of a lunar gravity assist seems to save about .5 km/s -- 3.5 km/s...

I'm hoping people will use Farquhar's 9 day, 3.5 km/s path from LEO to EML2: The path is time reversible so it'd also be possible to do a .147 burn to drop from apolune to a perilune deep in the moon's gravity well. At perilune exploit the Oberth benefit and do a .184 km/s burn that sends the...

Yes, I think those are the major considerations. Make the plane change too far from launch and and the transfer plane can swing quite a ways from departure and destination planes. But plane change expense further out is lessened by slower velocities. I'm pretty sure the plane change should be...

That's me, thanks! :) The Cosmic Train Schedule is based on circular, coplanar orbits. Since orbits are actually elliptical and inclined, that model can give poor approximations at times. If you browse through some of the stuff at that page, you'll see I'm trying to come up with ways to deal...

For Hohmann transfers to an inclined orbit, Lambert iterations tend to give polar transfer orbits! This results in huge plane change expense at both ends, destroying the Hohmann transfer's advantage. A midcourse plane change can take much of the ridge out of the porkchop plot. But what is the...

I believe both these tools solve Lambert's problem to get the delta Vs. A Hohmann orbit traverses 180 degrees between departure and destination. Unless departure happens to be on an ascending or descending node, the Lambert triangle would have to be at right angles to the departure orbit and...

My pleasure! I've always enjoyed playing with conic sections. It's a good idea to check my work. There were 4 or 5 steps between the law of cosines and the last equation and I'm prone to making stupid copying errors.

Start with a coordinate system that puts perihelion on x axis and the sun at the origin Position vector is |r| * ( cos(f), sin(f) ) Now draw a line segment to 2nd focus. Call angle F2 P F1 alpha The velocity vector lies on the tangent line at point P. Using a well known reflective...

It is you comparing I.S.S. to a Mars base. When I mentioned a permanent human presence on Mars is not sustainable without trade or return on investment, you cited ISS as a counter example. This is like saying since I can permanently maintain a dog without ROI, I can do the same for an...

Gravity loss would be a problem if your SSTO uses hydrolox. Another problem is achieving the achieving the tiny dry mass/fully loaded mass fraction needed to achieve a delta V budget. It wouldn't be possible to enclose 3363 cubic meters of hydrogen with the mass you allocate. When delta V...

For vertical ascent to upper atmosphere, kerosene's better. For achieving orbital (or escape velocity) above earth's atmosphere, hydrolox is better. Unfortunately with single stage it's hard to have both. Having two types of propellant and two types of rocket engines in the same stage would...