On Sat, 5 Mar 2005 07:29:57 -0800, "Rich S."
wrote:

But what I *really* wanted to explore was design ideas for a homebuilt
"airborne" Moon vehicle.

Here's the scene: You're living on Luna, having retired from ______ (fill in
blanks at your pleasure). It's the year ____ and low-gravity retirement has
become the "in" thing. You live longer, the old aches and pains are less,
etc. Your Social Security private trust fund has built up to the point that
you just *have* to start spending some of it! The one thing you miss since
moving out here is roaring around in your homebuilt on Saturday afternoons.
So, absent any regulation to the contrary, you decide to build a Lunar
replacement.

"Moon Zero Two", 1969, starring James Olson.

First thing to decide on is a name for the critter. Hmmm..... Moonraker
sounds appropriate. Wonder if anybody has used that one?

Been there, done that:

http://www.bowersflybaby.com/stories/leoraker.JPG

Oh heck with that,
let's get on to the design parameters.

Seats - One, two???

With a weight increase, the amount of fuel needed increases disproportionately.
Also, if you add a second seat, you're always going to have to have a body or
ballast in the spot to keep the beast in balance.

Pressurization - (?) if not, then a big enough seat to accommodate a space
suit.

It's tough to do precision work in a space suit. The gloves give you next to no
tactile feel...in fact, the fingertips are usually covered with hard rubber
shells.

http://www.hightechscience.org/orlan_space_glove.htm

You're not going to be able to work a keyboard, and if you have buttons and
whatnot to push, they're going to have to be well separated to ensure you don't
punch the wrong one. It's gonna be tough to fly without a pressurized cabin.

But...again, pressurization is going to add a lot of weight. You not only need
a pressure hull with windows and an openable door, but you're going to need the
typical air conditioning functions such as oxygen replacement, CO2 removal,
humidity control, etc. Since these problems are ALREADY solved with a space
suit, you might as well just go open cockpit...after all, you'll need a space
suit onboard anyway for the walk from the landing field to the cafe for that
$100,000,000 hamburger.

Hmmmm, single seat, open cockpit. The Luna Baby? :-)

Range - There's fuel and air caches every 1,800 miles, so let's add ~10% and
say 2,000 miles.

2000 miles is about 1/3 the way around the entire moon...2/3rds the maximum
distance you'd want to fly, anyway.

It's been years since I did any sort of lunar orbit work (and even that was only
for a week or so...damned if I can even remember what program it was). To get
some answers, I modified one of my orbit analysis tools to do Moon orbits
(changed the values for G, planetary radius, and gravitational constant). In
other words, lotsa approximations here.

For a 2000-mile ballistic trajectory on the Moon that gets at least 10 NM high,
you'll need about 5000 FPS of acceleration. And if you want to touch down with
near-zero speed, you'll need about the same for deceleration. We'll call it a
total of 10,000 FPS. Flight time less than a half hour, including accel and
decel.

Let's assume an open-cockpit single-seater. Call it 200 lbs for the pilot,
another 100 lbs for his suit, 500 pounds of airframe, 20 pounds of avionics, and
50 pounds for batteries and life support supplied. Let's assume our rocket fuel
has a specific impulse of 250 seconds. That's a dry weight of about 870 pounds.

The fuel comes out to another 2150 pounds.

Like Robert said, though, we could use a mass driver or other ground-based
system to throw the vehicle, and just rely on onboard fuel to land. This drops
the required onboard fuel to about 750 pounds. Not too bad.

Speed - Let's say 600 knots. (What I'm doing is multiplying typical terran
specs by 6. Why? I dunno)

Visible means of support (Lift) - Wonder if NASA has an airfoil for an
airless environment? If not, we'll have to come up with something. I
wouldn't want to go ballistic - it's not as much fun as low & slow.

Yep, ballistic wouldn't be much fun. You want a "Hollywood" moon flight: Take
off, climb to a given altitude, cruise at that altitude through the entire
flight, then descend to land.

If we don't have antigravity, what's it going to take?

Let's look at the cruise speed first. 600 knots is about 1000 FPS, and we'll
need both acceleration and deceleration fuel. Total 2000 FPS. Give it another
500 FPS to cover the climb (coming down is free!).

To fly at the constant altitude, we'll need constant downward thrust to
counteract the force of gravity. Since we're flying 2000 NM at 600 knots, we
have to do this for about 3.3 hours. Call it four hours with VFR reserves. :-)

So...we have to burn our downward thrusters for four hours. "G" on the Moon is
about 5.6 ft/Sec^2. We'd need to burn the same to counter that. Total
acceleration required is 5.6 ft/sec^2 x 4 hours x 3600 seconds/hour... about
80,000 FPS, about sixteen times more than a ballistic S/C using a mass driver
for launch, and, as a point of interest, almost three times what a spacecraft
launch from the *Earth* needs. With the accel/decel Delta-V, our 870-pound
spacecraft requires 24.9 *million* pounds of fuel.

C'mon guys. There's got to be another Rutan out there. What are we going to
do when he's history?

Live far more boring lives, I reckon....

Ron Wanttaja