Hermes Shuttle Overall Design

Alright, first post here.

So here we go:
First project I'm going to reveal is the Hermes Shuttle, named after the Greek messenger "...He was protector and patron of travelers, herdsmen, thieves, orators and wit, literature and poets, athletics and sports, invention and trade..."

The Hermes is more sci fi, and thus I'm allowing myself more advanced technology for this one than I would for other projects.

It's mission is to allow surface expeditions to alien worlds. It travels interstellar docked to a dedicated ISV "Mothership", from there it undocks in orbit over the world, is to be able to maneuver in orbit, perform EDL, and take off again without any ground infrastructure whatsoever, not even a runway.

The worlds it will expedite exploration of are Earth-like worlds.



This first post will be dedicated to the overall design of the vehicle.

First - the take off and landing style.

While initially, a Vertical Take Off or Landing (VTOL) design might be the most attractive option, under further consideration I don't see it working:  the vehicle must be able to deploy rovers and "set up camp" relatively rapidly. While a VTOL configuration would allow landing in small clearings, it would also restrict the orientation of the payload bay, and by necessity the Main Propulsion System (MPS) must be underneath it, which would mean using cranes and elevators to move every and any bit of cargo out of the payload bay.

Not to mention, our design necessitates very high thrust powers, which in a VTOL configuration might scorch the ground rather intensely upon landing, maybe even cause forest fires on Earth or any worlds with vegetation, and make landing on ice entirely impossible.



So I've chosen Horizontal. It will make more sense once I show how the design works...

Horizontal landing... Without a runway?

There's two options, here.

#1:
I can stay on land, but it would require some very tough landing gear and a large opening.

With the correct design, lots of airbrakes, a very high lift coefficient with flaps and slats all the way down, a pre-landing flare maneuver and perhaps even high-thrust retrofire from the RCS, it can be designed to land on a very short clearing.

And landing on land without a runway isn't something that's new. It would probably even simplify landing gear design. The Me-163 Komet, a German rocket plane (that's right: ROCKET, not jet!), a point-interceptor, landed in grassy fields using a sled-like landing gear [1,2]. Granted, it took off with wheels, but it didn't have a technology available the Hermes shuttle does: Thrust vectoring, and extremely high thrust (I'll cover the Hermes' rather unique MPS in a later post).

I'll return to the landing gear in more detail later, this post is supposed to be a more generalized overview of the vehicle.

#2:
Or I can go on water. Assuming the planetary body has significant water, boatplanes have, since their creation, landed and taken off from water bodies.

The major problem here, though, is getting landing gear that can do this, and yet stay tucked safely under the heat shield during entry.

My solution: Inflatable landing gear.

A very strong kevlar-like material, with an inner airtight layer to allow inflation upon deployment. The tricky part is it'll have to deflate and stow again.



The solution I've chosen here, is to make the landing gear adaptable. The gear consists of the bays, doors, mechanical extending, locking, and suspension system. On the end of this is an adapter upon which can be installed either a folding landing skid, or the inflatable floats for water landing.

Back to Overall Design

A picture is truly worth a thousand words, so forgive my artistic skills, but I believe the best way to approach the overall design - now that we've established an airplane-like HTOL configuration - is starting here:

Hi-Res Link

NOTE: As of yet, I have no pixel-by-pixel scale accurate design of the vehicle, and I will not and can not until I have calculated the masses of various systems and their performance.

For now, this is only meant to illustrate the general layout of the vehicle and the position of various systems in relation to eachother, although it's scale is not accurate.

-My only requirement for scale is that the payload bay be 9 feet in radius, with a flat bottom. as to accommodate vehicles and equipment for expeditions, and a flight deck and mid-deck that can sustain a crew of 7 for three weeks



One of the main reasons I chose this design is the rapid access to and deployment of cargo.
With this, it is possible to open a door, and drive a rover right out of the cargo bay, or fly a VTOL aircraft (such as a helicopter or jet-helicopter) straight out, as the surface expedition requires.
Take a look:

While most of the payload bay opens in a manner akin to the Space Shuttle, a section on each side can open into a full-fledged ramp.

A closer look:

The upper portion rotates independently.

To allow a vehicle to directly roll off, aluminum-lithium beams are stored in a folded-up position (A) and can deploy and lock into a ramp that vehicles can traverse (B).

Cables also provide addition strength, and can be reeled in to assist in closing the door under gravity.

The Main Propulsion System

For the MPS, I chose a design of my own.

Notice the fuel tanks are very small - fuel in the technical sense, that is the material, a fluid in this case (thought not necessarily liquid in use), that provides the energy. The reaction mass, on the other hand, is stored in the massive tank in the back, central fuselage.

Like the original VASIMR concept, the engine can vary specific impulse and thrust. However, it has one key advantage over VASIMR that makes significant thrust possible:

Conditions for fusion reaction require extremely high temperatures. In order to put enough fuel through a fusion engine to create significant thrust, would require an absolutely enormous amount of energy, and thus enormous engine, so that more thrust would be needed.

In the end, conceivable Fusion engines by themselves (that is, in the forseeable future) cannot provide enough thrust/weight to get a vehicle off of the ground, and if they could, the waste heat would be astronomical, probably far more than any vehicle could deal with.

So the system here is a bit different. Instead of running all the reaction mass through the combustion chamber, the combustion chamber, based off of and arranged as a Gasdynamic Mirror Fusion engine, produces the energy via fusion, and has an exhaust section.

In the exhaust section, is a ring with high-pressure sprayers that inject the reaction mass into the exhaust stream.

By kinetic collision and a very high-strength injection chamber, the exhaust from the fusion portion of the engine transfers energy, in the form of thermal and kinetic energy, into the injected fluid.

The result is a trade-off. More thrust is gained, but at the cost of Specific Impulse (ISP).

The idea is that during the ascent, during takeoff and the initial climb against gravity, the engine operates in an extremely high-thrust mode, but as it accelerates, the vehicle will feel the gravity of the body it's accelerating from less and less.

Equations here:

g = u/r^2
where u is Earth's mass times the gravitational constant, G, and r is the distance from the vehicle to the planet's core.

The gravity the vehicle will have to overcome is:
a = g - v^2/r

v^2/r is the equation for centrifugal force. Once the vehicle is going orbital velocity, the two cancel, and it no longer falls towards the planet.

But, as it gets closer and closer to that speed, it no longer has to thrust as much to overcome gravity.

As such, during the ascent, the rate at which reaction mass is injected into the fusion engine's exhaust stream can decrease, increasing the efficiency of the engine, and thus allowing for a much smaller amount of propellant.

Also, with zero injection, the fusion engines have a tremendous ISP for orbital maneuvering.

- I'll come back to the MPS system in more detail and explanation later, in it's own dedicated post. But for now, I must move on to cover other aspects of design.




Notice in the drawing above, that the wing shape makes two triangles.

Wing Shape

During atmospheric re-entry, Flow Separation is very significant. What this is, is the air is at such an angle that it no longer flows over the top of the wing, making it so the wing no longer produces lift, but acts like a brake. Obviously, throwing a wing bottom-first through the air will just create a lot of drag. So there's a certain angle where the flow separates.

The longer the wing, the shallower the angle.

So a delta-wing shape is perfect for atmospheric re-entry, where you want to carefully control how much flow separation you have. If you have too much lift, you'll skim off the atmosphere, and then come plummeting down again too fast and burn up (think of skipping a stone - it goes up that last time, then comes in the last time too steep and it splashes straight into the water instead of skimming. Kind of like that, if you skim off of the atmosphere, you'll come back too steep and burn up) if you have too little lift, you'll descent too fast and burn up.

So by pitching up and down, the shuttle can change how much lift it has, and also change how much drag it has (because pitched up, more area is dragging against the air, much like the difference in-between standing on a bike at high speed, or curling down to reduce drag).

So you see, at A. the wing is shorter, and so the air easily flows over and creates lift. But at B, the wing is too long for the angle it's at, and instead of smoothly flowing over, it overshoots and there's flow separation.

So because of triangle-shaped wings, the higher you pitch, you gradually lose lift at a controlled rate.

Summary:

Well, that's all I have for now. I'm eager to delve into the Main Propulsion System later in another post, but for now, I hope you enjoyed. Feel free to comment, message, and otherwise discuss the design.

I do realize it's an advanced and complex design - I will be doing other projects that are much nearer term technology, but I decided this would be the best to start off my blog with ;)