General Question Manoeuvering around on Phobos, and landing on Mars

[cr1]

Two questions...

1. Due to Phobos' irregular shape, I do not seem to be able to "drive around" with my DGIV on it... It either starts "taking off" by itself (and then escaping Phobos' gravity) or does some weird things like the Surface MFD indicating 0.00km altitude while I seem floating (in the air) in space in exterior view.
(For driving around I mean like driving a car, with the wheels in constant contact with the ground).

Is there any way to "drive" my DGIV on Phobos?

2. Can we land a DGIV on Mars the way we land an airplane on a runway? I've tried taking off and turning around like an airplane does but I suppose Mars' atmosphere is too thin to make my control surfaces work, and also too thin to make my DGIV act like an airplane rather than a fuel-powered rock. Are landing pads and retro/hover/RCS engines the only way to land the DGIV on Mars?

Thanks for answers!

 

[Urwumpe]

Two questions...

1. Due to Phobos' irregular shape, I do not seem to be able to "drive around" with my DGIV on it... It either starts "taking off" by itself (and then escaping Phobos' gravity) or does some weird things like the Surface MFD indicating 0.00km altitude while I seem floating in the air in exterior view.
(For driving around I mean like driving a car, with the wheels in constant contact with the ground).

Is there any way to "drive" my DGIV on Phobos?

Congratulations, you have found out that for Orbiter, all celestial objects are spheres - even if they no longer look like that.

I think Orulex was fixing this.

 

[TJohns]

1) Phobos & Deimos are RENDERED with a 3D mesh so they appear to have irregular shapes with hills, valleys, craters, etc. However, they are MODELLED as a regular sphere with a constant radius. It's this "invisible" sphere that Orbiter uses for determining where the "ground" is (i.e. where the wheels sit), not the mesh that might be 100's of metres above/below you. Also, the gravity of Phobos is so weak that the escape velocity is only a few m/sec, so if you move at any decent rate you've already taken off!

2) For an interesting discussion on Martian flight see http://www.x-plane.com/mars.html

Trevor

 

[andysim]

There was a episode of the BBC Odyssy program where they used a harpoon to fire a securing line into the surface of a small body so they didnt drift off -) (cant remeber which) but any small moon is going to have this problem.


At 2 mins 50s -)

 

[cr1]

1. Ok... so it is going to be difficult driving around Phobos in Orbiter and in real life so I'll abandon that idea (that securing line idea wasn't too bad tho)
Wikipedia says Phobos' Escape velocity is 11.3 m/s (40 km/h)! How sad...
http://en.wikipedia.org/wiki/Phobos_(moon)


2. The X-Plane article is quite interesting (even though it hurt my eyes and my brain going thru the mixture of upper- and lower-case letters ). Apparently Mach 1 (~244.2m/s on Mars? http://www.aerospaceweb.org/question/atmosphere/q0249.shtml) is the minimum speed needed to fly... Turning around while flying is difficult due to high inertia... Landing also needs a high speed but air drag and ground friction are not enough to slow you down after touchdown...
Since we have hover engines on Delta Gliders, those could be useful to make us land at a slower speed (turning on hovers at ~25%?). Building longer runways (~6km?) so that you have enough distance for slowing down might also help (the X-Planer had to use a 3km long runway with arresting wires). There's also the reverse thrusters to help slowing down after touchdown (hopefully the retro covers won't get blown off). The Delta Gliders' main engines are much more powerful than the X-Planer's engines, so to turn around in mid-flight, we could throttle down the engines, turn around to the heading we wish to go to (using RCS and control surfaces), and then turn them back to full power again.
Any other suggestions for turning around and landing for Mars atmospheric flight?


Sorry if my English isn't that perfect... This is what usually happens to me when I type long posts.


EDIT: Are there loud sonic booms on Mars?

 

[C3PO]

Wikipedia says Phobos' Escape velocity is 11.3 m/s (40 km/h)! How sad...

That's not sad. It means that transportation on Phobos is almost "free". You can 'fly' around the place using small thrusters.:speakcool:

 

[Urwumpe]

That's not sad. It means that transportation on Phobos is almost "free". You can 'fly' around the place using small thrusters.:speakcool:

Especially, even a UMMU astronaut can escape from Phobos.

 

[Jarvitä]

To fly on Mars at least somewhat like you would on Earth, you'd need an aircraft with huge wings (think gliders, but larger), and probably arresting gear in order to land at 300 m/s.

 

[cjp]

Any other suggestions for turning around and landing for Mars atmospheric flight?

I recently developed a Delta Glider flying skill which could be described as "hover engine assisted atmospheric flight".

The basic idea is to use your hover engines when you don't have enough lift, e.g. because your speed is too low, or the air is not dense enough. I even use it on earth, when I have enough fuel, because it allows me to have an incredibly low runway approach speed. Basically, such an approach is a hybrid between a vertical landing on hover engines, and a normal horizontal landing.

The same should also be possible on Mars. Steering even works a bit similar to normal atmospheric flight (e.g. roll to the left and you'll accelerate to the left), because the hovers work a bit like lift from the wings.

The most important difference between atmospheric flight and vacuum flight is that in the atmosphere, the Delta Glider (like any aircraft) tends to automatically points its nose to its forward direction of motion. This allows for controlling it intuitively. Flying in vacuum doesn't have this, and my hover assisted flight is somewhere in-between. You may have to actively use your pitch and yaw RCS to point the nose in the right direction.

I tried "vacuum-style" flying on Mars, but with this the atmosphere can actually be annoying. For instance, when flying fast, it's difficult to point the nose in an arbitrary direction, so you first have to slow down.

 

[T.Neo]

Basically, such an approach is a hybrid between a vertical landing on hover engines, and a normal horizontal landing.

STOVL?

 

[cjp]

STOVL?

Maybe HTOSL or STOSL. Or, if you want to use a landing pad instead of a runway, it will be VTOVL.

I use it on earth because runway landing becomes a lot easier when you can slow down more. But I see the similarity with airplanes like the Harrier or the JSF.

 

[RisingFury]

That's not sad. It means that transportation on Phobos is almost "free". You can 'fly' around the place using small thrusters.:speakcool:

Thrusters?

If you jump hard enough, it's likely you'll never return

Maybe HTOSL or STOSL. Or, if you want to use a landing pad instead of a runway, it will be VTOVL.

VTOL = Vertical take off and landing

 

[TMac3000]

Where can I get a full episode of that TV show? That looks amazing!

 

[T.Neo]

Where can I get a full episode of that TV show? That looks amazing!

It is from the BBC. I think you can buy it on DVD.

 

[Calsir]

There was a episode of the BBC Odyssy program where they used a harpoon to fire a securing line into the surface of a small body so they didnt drift off -) (cant remeber which) but any small moon is going to have this problem.

1. It's like ESA Rosetta mission, where the Philae lander will attach itself to the surface of the comet by firing two harpoons and reeling in. Of course, the lander has a much more difficult task than an explorer on phobos, as the solar wind can literaly sublimize the ground on whitch it stands . Also, don't forget about Mars gravity. I recall one of the introductory DG or DGIV scenarios, where you were to fly around one of Saturn moons whose sphere of influence lied _beneath_ its surface. Quite messy.

2. If you design an aircraft (CO2craft?!) with wide enough and high aspect ratio wings you can take off at slow speeds (M<1), especially since the weight your wings have to lift is only 4/10. Of course, martian air density is about .02 kg/m3, around 1/1000 of earth sea level density. Also, I don't think we want to take off or land at supersonic speeds, it can get too interesting. Besides, you still need an engine that can work in the CO2 prevalent atmosphere, like an electric propelle or a rocket.

I use it on earth because runway landing becomes a lot easier when you can slow down more. But I see the similarity with airplanes like the Harrier or the JSF.

There is one trouble, as it is very hard to control a ship using the hover thruster without autopilot. Try the ummu tutorial about ground hovering, for instance.

 

[cjp]

There is one trouble, as it is very hard to control a ship using the hover thruster without autopilot. Try the ummu tutorial about ground hovering, for instance.

I usually allow myself to use the built-in autopilots, like HorLvl and KilRot. Do you think I should try without?

I don't have a joystick BTW. I'm even using a laptop, so I have a numeric keypad accessible with the Fn key.

 

[RisingFury]

There is one trouble, as it is very hard to control a ship using the hover thruster without autopilot. Try the ummu tutorial about ground hovering, for instance.

No, not really... when not in the 2D panel view, the upper left display that shows the thrust will show you the acceleration of the main/hover engines. 9.8 will match Earth's surface gravity and prevent you from going up or down. A slight tap on "," key will decrease the thrust slightly so you can land slowly. Keep in mind that as you burn fuel, you become lighter and thus the acceleration becomes greater.

 

[Calsir]

I usually allow myself to use the built-in autopilots, like HorLvl and KilRot. Do you think I should try without?

I don't have a joystick BTW. I'm even using a laptop, so I have a numeric keypad accessible with the Fn key.

Try to fly without them only to understand how it works. Using orbiter on a laptop: I know your pain and the Fn nightmare, I have been there. Now I use an external keyboard, albeit with no joystick.

No, not really... when not in the 2D panel view, the upper left display that shows the thrust will show you the acceleration of the main/hover engines. 9.8 will match Earth's surface gravity and prevent you from going up or down. A slight tap on "," key will decrease the thrust slightly so you can land slowly. Keep in mind that as you burn fuel, you become lighter and thus the acceleration becomes greater.

I am not complaining about the difficulty keeping altitude, during hover, but manoeuvring the ship like an helicopter, with the added difficulty of having to use the RCS for attitude control. The input does not control the angular velocities (like on a plane, for instance) but the angular acceleration. It is a second order control and we human have hard times with second order instrumentation, on the whole. Besides, it tends to be unstable since the resulting thrust lies below the centre of gravity.

 

[cjp]

I am not complaining about the difficulty keeping altitude, during hover, but manoeuvring the ship like an helicopter, with the added difficulty of having to use the RCS for attitude control. The input does not control the angular velocities (like on a plane, for instance) but the angular acceleration. It is a second order control and we human have hard times with second order instrumentation, on the whole. Besides, it tends to be unstable since the resulting thrust lies below the centre of gravity.

I tried flying without autopilots (on the laptop). It's difficult, but yes, it is doable. I landed on a runway on Mars, but unfortunately something went wrong after touch-down, and my rudder didn't go back to neutral, so the ship steered off the runway. But my speed was so low I don't think it would have been fatal.

Yes, steering with RCS is the main problem, especially when there's not enough atmosphere to damp out rotations. I tried my hover-assisted maneuvring on Mars, but turning the ship 180 degrees is very slow. It's a lot easier to simply slow down (either retro-rockets or pitching up), point the nose to where you want to go, and accelerate again.

Using the hover engines on the DG in Orbiter doesn't make you very unstable, but this is probably different from the real world. It would be nice if Orbiter simulated small fluctuations in the thrust level and direction of engines, to see whether that makes a difference.

 

[HiPotOk1978]

I have spent many hours flying in the martian atmosphere and it can be very tricky at lower speeds even with a joystick. Of course there are very few places in the solar system where 1800ms at 3km altitude will not turn your beautiful shinny ship into a blacken charred hulk. A few things to think about when your flying on Mars is that high speeds are required to produce enough lift with a DGIV wings. Vertical speed is your friend and enemy, it is easier to produce lift with thrust than with an airfoil especially during a landing. Your not going to consume as much fuel with vertical or main engines as you would on Earth cause of the lower gravity and atmosphere pressures. You can open those aerodynamic doors at high speeds cause your dynamic pressures are going to be lower. Air brakes are pretty much useless unless your diving into the atmosphere during a reentry and wanting to slow yourself enough for use of the retro engines.