Jool 5 route.

[qzgy]

Hello. So I am trying to do a jool 5 at the moment, and am currently in the joolian system. I have a spaceplane with around 5000 dV on NERVs and around 7000 units of oxidizer for rapiers/VTOL vectors. Oh, and an ISRU system.

At the moment I'm stuck. I've visited Pol and Laythe with minimal issues. However, I'm not sure where to go from there, or actually how to land on Tylo or Vall with a sorry 0.2 or so TWR on NERVs, fully loaded. Can anyone help/give tips on landings and a possible route?

Thanks.

Craft for reference. https://kerbalx.com/qzgy/Heidegger-V

I already ditched the rover as well.

[Aegolius13]

If you have ISRU and are not staging, you have pretty wide latitude in terms of what order to do.   One issue is that Tylo and Lay the can grab you during maneuvers,  and that cab be minimized by doing the planets in order (e.g, Laythe to Tylo to Vall to Bop to Pol).

Tylo sounds potentially tough.   You cannot land or take off with a local TWR under 1, and gravity there is not much less than Kerbin.  So you you may have to go partly fueled to lighten your ship.   You can use your Rapiers in rocket mode for more thrust,  but not sure what that will do to your dv total.

[qzgy]

1 hour ago, Aegolius13 said:

If you have ISRU and are not staging, you have pretty wide latitude in terms of what order to do.   One issue is that Tylo and Lay the can grab you during maneuvers,  and that cab be minimized by doing the planets in order (e.g, Laythe to Tylo to Vall to Bop to Pol).

Tylo sounds potentially tough.   You cannot land or take off with a local TWR under 1, and gravity there is not much less than Kerbin.  So you you may have to go partly fueled to lighten your ship.   You can use your Rapiers in rocket mode for more thrust,  but not sure what that will do to your dv total.

Yeah, probably the best thing to do is to go partially fueled. I was coming from Pol very heavy, almost a full load. Might then just head to bop to burn some LF.

As for deltaV - I might not have enough on RAPIERs, but have plenty on nervs. Then again, the TWR problem appears....

Craft redesign may be in order...

 

Looking at the craft in the SPH, I can MAX get 1500 m/s out of the VTOL vectors.... Don' think that's enough right?

Unless I do some crazy stuff like using brakes to slow down.......

Edited June 7, 2017 by qzgy

[Aegolius13]

2 hours ago, qzgy said:

Yeah, probably the best thing to do is to go partially fueled. I was coming from Pol very heavy, almost a full load. Might then just head to bop to burn some LF.

As for deltaV - I might not have enough on RAPIERs, but have plenty on nervs. Then again, the TWR problem appears....

Craft redesign may be in order...

 

Looking at the craft in the SPH, I can MAX get 1500 m/s out of the VTOL vectors.... Don' think that's enough right?

Unless I do some crazy stuff like using brakes to slow down.......

Yeah, 1500 m/s is not enough to land on Tylo.  But is that with none, or some, or all of the liquid fuel for your nukes?  If you can get more delta-v with less liquid fuel, that might work.  

Also, maybe you can do a hybrid approach - start the deborbit with the nukes, burn them as long as possible, then change to chemical rockets towards the end. You could also look at using the Rapiers rather than the Vectors for this portion, so you can keep utilizing the nukes.  But just a lot of variables at work here; it may take some field testing to see if there's a combo of TWR and delta-v that works.  

If you go the route of a redesign, I wonder if it would be better to just ditch the nukes, and go with Rapiers for Kerbin/Laythe, plus the Vectors for VTOL and general purpose vacuum thrust, and maybe sub out some of your LF tankage for LFO (keeping just enough to run your Rapiers on jet mode).  Tylo is probably the most demanding single leg of the trip for both TWR and total delta-v.  So to paraphrase Sinatra, if you can make it there with just chemical rockets (getting, say, 3000-3500 m/s with no surplus liquid fuel on hand) you can make it anywhere.  The potential 5000 m/s on your nukes may be overkill if you never need to go the full 5000 between refuel stops.

 

[qzgy]

50 minutes ago, Aegolius13 said:

Yeah, 1500 m/s is not enough to land on Tylo.  But is that with none, or some, or all of the liquid fuel for your nukes?  If you can get more delta-v with less liquid fuel, that might work.  

Also, maybe you can do a hybrid approach - start the deborbit with the nukes, burn them as long as possible, then change to chemical rockets towards the end. You could also look at using the Rapiers rather than the Vectors for this portion, so you can keep utilizing the nukes.  But just a lot of variables at work here; it may take some field testing to see if there's a combo of TWR and delta-v that works.  

If you go the route of a redesign, I wonder if it would be better to just ditch the nukes, and go with Rapiers for Kerbin/Laythe, plus the Vectors for VTOL and general purpose vacuum thrust, and maybe sub out some of your LF tankage for LFO (keeping just enough to run your Rapiers on jet mode).  Tylo is probably the most demanding single leg of the trip for both TWR and total delta-v.  So to paraphrase Sinatra, if you can make it there with just chemical rockets (getting, say, 3000-3500 m/s with no surplus liquid fuel on hand) you can make it anywhere.  The potential 5000 m/s on your nukes may be overkill if you never need to go the full 5000 between refuel stops.

 

The 1500 m/s is without any LF for the nukes. So yeah, using the vectors is out of the question.

I'll have to play around with the hybrid approach. Using the rapiers instead might be a better option, especially since the vectors are not well balanced. Also, seems the rapiers have less than a 0.8 TWR...

I'm not super enthusiastic about a redesign. But yeah, you are probably right about 5000 m/s being overkill. I'll keep your comments in mind if I do a redesign.

EDIT:Another question. For both the Tylo/Vall landings, is it better to start in a high orbit or in a lower orbit?

Edited June 7, 2017 by qzgy

[Aegolius13]

1 hour ago, qzgy said:

EDIT:Another question. For both the Tylo/Vall landings, is it better to start in a high orbit or in a lower orbit?

A lower starting orbit uses less delta-v, but if your TWR is not high enough,you might crash before you can stop your downward velocity.  Going from a higher orbit can buy weaker engines more time to do this.  So the ideal is the lowest that your design can survive.  

[qzgy]

What I might do is pack a separate Tylo lander in the cargo bay. Minimizes the need for redesign. I also already have enough dV, so why not use it?

[Jouni]

9 hours ago, qzgy said:

EDIT:Another question. For both the Tylo/Vall landings, is it better to start in a high orbit or in a lower orbit?

I usually start Tylo landings from a 30 km orbit, and begin the final burn at around 20 km. The idea is to keep the descent rate at around 100 m/s. This gives you around three minutes to get rid of both horizontal speed and altitude, and then you can land without spending too much fuel for controlling the vertical descent.

If you start too low, you may crash because you can't kill the horizontal speed in time. On the other hand, if you start too high, you may kill the horizontal speed too soon, and then you may run out of fuel during the vertical descent.