Thanks DaveS, I know that in real wold helium is used as an inert gas and to keep the fuel-tanks under pressure.(HE is nice for this, it doesn't burn and it does not re-act with other elements).
But, for this ship, this can be found within the SCN description:
"Use "J" to grapple the extra 4He container for an extra 105to of fuel for the Ion drives."
...Which I have done, and its on board, but I cannot do anything with it at the moment.
I.e. re-fill HE doesn't work.
My guess is, that the internal HE-tank is still full at 100 perent, so a re-fuel cannot work.
...so I would have a look through the manual for this.
I mentioned this allready, that I cannot find anything related to HE/ION-engines-usage within the provided doc.
My guess is, that the reactor needs to be started, but how ?
Ok, however, after I found no way to use the IONs, I decided to make a reentry, which ended in a desaster:
The ship seems to have zero drag, so I tried the AUX engines in revert-mode to slow down.
The the AUX enines alone have not enough thust to slow down the ship.
So I crashed with about 6500 m/s into the ground.
So the doc seems to be missing two important ponts:
1. how to use the ION engines
2. a strategy how to perform a controlled reentry.
Edit:
For point 1:
I rechecked the Firehawk doc, and here the key for starting the reactor is "p".
This works with the "Star-Clipper", too.
So to activate the ION engines, one has to press "p" to acticate the HE-driven-reactor.
Then "+" controlls the ION engines.
For reentry PursuitMFD might be helpfull, but I doubt that there is enough main-fuel to slow the ship down and land. (without any help from the atmosphere to slow down).
Edit2:
I found a way for a complete automated reentry+landing:
-While in Orbit, make sure to have small cross-range to the base...as usual
-Make sure the main-fuel-tanks are at 100 percent (i.e. sent a tanker to re-fuel before planning the de-orbit)
-set AUX-engines to HOVER-Mode
-use PursuitMFD's landing mode
-enjoy the show (I have had a burn-time until touchdown at about 1700 seconds...so it takes a while)
-dont't forget the landing gear....
-right before touchdown, switch off PursuitMFD, which results in a HOVER-off and and the landing is very harsh
Otherwise PusruitMFD will try to over-correct the vessel-position and could lead to wild oscillations.
-check your fuel after landing....not much left
While PursuitMFD is running, there will be an endless beep-beep-beep-sound-loop.
You can avoid this, if powering-down the MFD (red button...don't worry PursuitMFD will continue its job....but no more beeps).