Hohmann orbits, Launch windows, delta vees etc.

Recent conversations with Henry Spencer and James Nicoll have opened my
eyes to a pleasing fact:

It can cost much less delta vee to do a periapsis burn low in a gravity
well and capture a body to highly eccentric elliptical orbit. I had been
capturing bodies to circular parking orbits.

So I have made some changes to my Hohmann.xls spreadsheet. Instead of
entering altitude of circular parking orbit, the sheet now asks for
periapsis and apoapsis altitudes of the parking orbit.

If the user wishes, he (or she) can still get delta vee for capture to a
circular orbit: Just make the apo & periapsis the same altitude.

I've also added the planet's Sphere Of Influence. The apoapsis should
lie within the SOI for capture. The cell to the right of the apoapsis
gives the number it shouldn't exceed.

The spreadsheet has all the planets but Pluto. It gives synodic period,
Hohmann trip time, launch windows and some other stuff.

To download go to http://clowder.net/hop/railroad/sched.html
and a link for Hohmann.xls is just underneath a table near the top of
the page. Windows users can download with a right click, Mac users with
a sustained click.

I'm hoping some ssp readers find this useful for BOTECs. I also hope
some of the knowledgeable folks here will take a look & let me know if
there are errors in the spreadsheet.

--
Hop David
http://clowder.net/hop/index.html

On Thu, 16 Sep 2004 17:30:30 -0700, Hop David
wrote:

So I have made some changes to my Hohmann.xls spreadsheet. Instead of
entering altitude of circular parking orbit, the sheet now asks for
periapsis and apoapsis altitudes of the parking orbit.

Out of curiosity, can the spreadsheet be modified to add
trans-lunar trajectories? I've been wanting to find the delta-vees
for:

Earth-orbit to Lunar-orbit
Lunar-orbit to Lunar-surface
Lunar-surface to Lunar-orbit
Lunar-orbit to Earth-orbit

Len Lekx wrote:
On Thu, 16 Sep 2004 17:30:30 -0700, Hop David
wrote:


So I have made some changes to my Hohmann.xls spreadsheet. Instead of
entering altitude of circular parking orbit, the sheet now asks for
periapsis and apoapsis altitudes of the parking orbit.


Out of curiosity, can the spreadsheet be modified to add
trans-lunar trajectories? I've been wanting to find the delta-vees
for:

Earth-orbit to Lunar-orbit
Lunar-orbit to Lunar-surface
Lunar-surface to Lunar-orbit
Lunar-orbit to Earth-orbit


Those things are of interest to me too. I'll take a stab at it.

I'm happy none of the above include Earth-surface because I don't know
how to deal with air resistance.

Maybe I'll have time to fool with it this weekend.

--
Hop David
http://clowder.net/hop/index.html

In article ,
Len Lekx wrote:

Out of curiosity, can the spreadsheet be modified to add
trans-lunar trajectories? I've been wanting to find the delta-vees
for:

From the now antique Cole and Cox's _Islands in Space_, the
bit with the space DC3 stats:

Earth-orbit to Lunar-orbit

12,000 ft/sec (3,600 m/s)

Lunar-orbit to Lunar-surface

8,000 ft/s (2,400 m/s)

Lunar-surface to Lunar-orbit

Should that be the same as above?

Lunar-orbit to Earth-orbit

12,000 ft/s (1,000 ft/s higher than for escape, for
some reason) (3,600 m/s)

I wonder how these values compare to modern calculations?
--
"I mean, you don't seem like a bad guy to me..."
"I don't? I got a death touch, an army of killer robots and a skull
drawn on my chest and I don't look like a bad guy to you? I think
you could be in the wrong business."

On Fri, 17 Sep 2004 15:14:41 -0700, Hop David
wrote:

trans-lunar trajectories? I've been wanting to find the delta-vees
Those things are of interest to me too. I'll take a stab at it.
I'm happy none of the above include Earth-surface because I don't know
how to deal with air resistance.

I know how to deal with it - start from orbit. :-)

Maybe I'll have time to fool with it this weekend.

No rush - I'll be working on my *own* rockets this weekend, and
might not have a lot of time to play with theoreticals.

On 17 Sep 2004 18:27:10 -0400, (James Nicoll)
wrote:

Earth-orbit to Lunar-orbit
12,000 ft/sec (3,600 m/s)

This includes braking into lunar orbit, yes...? :-)

Lunar-orbit to Earth-orbit
12,000 ft/s (1,000 ft/s higher than for escape, for
some reason) (3,600 m/s)

Must be for braking into orbit. I would've thought that injection
into Earth orbit would take more... then again, it takes that much to
get *out* of orbit, too.