Suborbit around the sun

[Falkenherz]

I know this has been asked a few times, but the treads I found did no give a full answer.

- Which distance to the sun counts as being in suborbit?

- How to achieve the cheapest momentary suborbit which I can inverse immediately? So far, I only found a retrograde ejection from Kerbin at about 6,000m/s deltaV.

- I can do those 6000m/s with a LV-N, if I can time the long burn times correctly. But how? I noted that if I burn >6 minutes, the whole orbit shifts while I accelerate and the deltaV prediction from the maneuver node is not necessarily accurate anymore.

Edited July 22, 2015 by Falkenherz

[SAI Peregrinus]

Distance is irrelevant. The trajectory just has to intercept the sun's surface.

Retrograde ejection from Kerbin is correct. Delta-V looks about right.

For low TWR rockets and long burns, I like to chain a few short burns. So make a node, get it to the point where it will be a short enough burn (< 1 minute), then make another node a bit further on the new orbit, etc. If you do it right you'll get a reasonable projection of where the single long burn will send you.

[AaronLS]

Distance is irrelevant.

600km is the altitude you need your periapsis to dip below to count as suborbital.

[Tatonf]

Indeed. That is because the Sun have an atmosphere starting à 600 000m.

[SAI Peregrinus]

600km is the altitude you need your periapsis to dip below to count as suborbital.

Yes, I said that. The distance your craft gets to is irrelevant. The altitude of perihelion is what matters. That has to intersect the "surface" of the sun's atmosphere, which is at 600km. This works for any other body: the periapsis of the orbit must intersect the surface of the atmosphere to be considered a suborbital trajectory, or the surface of the body if it has no atmosphere. Clearer?

[AaronLS]

Yes, I said that. The distance your craft gets to is irrelevant. The altitude of perihelion is what matters. That has to intersect the "surface" of the sun's atmosphere, which is at 600km. This works for any other body: the periapsis of the orbit must intersect the surface of the atmosphere to be considered a suborbital trajectory, or the surface of the body if it has no atmosphere. Clearer?

Yes, and just like any other body the altitude is relevant, or rather distance from the surface. Not sure why you chose to shoot down the OPs question in such a way as to call it "irrelevant" when he asked a very simple and straightforward question. Clearer? I was glad to followup and address his question with the specific altitude. Not sure what this reply hoped to add.

[Kryxal]

It's probably the point that you don't have to GO there, just be on the trajectory to get there for a few seconds.

[Falkenherz]

I was indeed looking for that figure of 600 km because I did not find it until now. I can now properly plan an instand-reversible suborbital trajectory. Thanks to you all for the very useful information!