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BenHR

Can I land on Tylo with this?

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I feel like I have barely enough fuel, if only I knew how to land in a more fuel efficient way. Is there such a way? Or do I not have enough fuel for any way?

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I dont know if i do it efficient enough but i bring periapsis just above terain near my desired landing site. Then just before i reach periaps slow down a bit to target said landing site. "Suicide" burn all the way to landing or lithobraking.

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Alright, step 1 is don't bother getting into a circular orbit before begininng your descent. Instead, combine your descent burn with your burn at periapsis to bring your apoapsis down. Also, don't cancel your horizontal velocity so high up, this gives gravity more time to pull you down, meaning you will be going faster higher. The best way to land on Tylo is a Suicide Burn.

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That's a very small lander for Tylo... I guess they're not expected to come home?

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I would also disable the engine's gimbal, if you're using SAS in retrograde mode - with all that wobbling, you're losing a bit of your precious delta-v.

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If I were you though, I'd use something like Girders as landing legs. It may look hideous, but 80 m/s is a big difference from 12.

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I suppose the shorter answer to your direct question is, "no, here use this ship instead and fly it like this", but if you let me and others walk you through the design process you will not only know how to land on Tylo, you will gain some skills that will help you do a lot of other things in the game as well.

First, do you know how much delta V you have in the lander when it's fully fueled? If not, post the mass with full tanks, mass with empty tanks, and we can show you how to calculate the dV you will get with your Poodle descent engine.

A perfect descent from orbit to Tylo surface costs about 3000 m/s delta V, and the same is true for the ascent. I suggest we start with the numbers and go from there. Depending on the dV of your craft and its thrust to weight ratio (TWR) we can make some suggestions of landing technique (i.e. vertical descent vs. constant altitude)

ETA: thanks Yukon for correcting, we need TWR not TMR when in Tylo SOI

Edited by Kuzzter
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Some says that with high TWR it can be done with 5500m/s. Never tried though ; only with low TWR.

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As for making a new ship, while the info is helpful, I'd like to land this one if I can for the time being. This flight was actually my first time aerobraking. I have no intention of bringing these guys back; my Treyciards have been used solely for one-way missions. So, a suicide burn is sorta what I was doing, burning retrograde the whole way down, and what I gotta figure out is setting up the initial trajectory and timing when to start the burn?

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As for making a new ship, while the info is helpful, I'd like to land this one if I can for the time being.

Might be able to help you with that if you give dV and TWR information, per my earlier post.

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Well, I'm at school right now, but I'll be sure to chalk those numbers up when I get home.

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Hmmm, I finally saw the video (locked from work). Your TWR seems to be very low. You can't just follow retrograde. You have to try to kill horizontal first while keeping vertical speed under control (less than 100m/s). You should use KER to display those figures. To do that, start quite low (under 30km) ; you must aim above retrograde, not on retrograde. The more you slow down, the more to must aim above retrograde.

But I'm bothered that your TWR could be too low. On your 2 first tries, your fuel tank was already very low and your ship was far from reasonable speed (600m/s left).

But on your last try, you where close. I noticed your altitude goes upward before going down. That's not a good idea, you loose deltaV. So keep going downward but with controlled vertical speed.

Also you aimed for Highlands. That's a good choice. It'll cost you less (vertical) deltaV to land and to take-off, thus I don't think you'll be able to escape Tylo.

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Well, I watched the video, did some calculations, and it seems to me you should be able to pull it off with that craft.

A side note: you are aware you can press G to toggle your landing legs, right? you don't need to individually select them.

Now, on to the dV related stuff:

* First: If you come in equatorial, you'll save ~18 m/s -> 2 seconds of hovering

* Second: Related to the above point. I hope you have an earlier save, where you can fine tune your trajectory so that your perapsis is much much closer to tylo. You are wasting so much dV on the capture burn and then lowering your perapsis (plus with that intercept... that is why you aren't equatorial)

* Third: your de-orbit burn is way too high -> get your perapsis even lower. You'll want to start your deorbit burn below 10 km (depending on terrain, it does go up to 11km on tylo, but you'll want to be even lower if it is 6km), not above 30

Now how to squeeze mor dV out of that thing...

You decouple a LV-N stage.

LV-Ns have 800 Isp, whereas the poodle has 390 Isp. In terms of dV per unit fuel, you'd get more keeping the dry mass and running the LV-Ns longer, until the dry mass of the upper stage is 390/800 x the total mass - ie when the LV-N stage is 410/800x the total craft mass.

I can't tell exactly what you have there, but I see:

1x empty orange tank: 4 tons

4x LV-Ns: 9 tons

1x hitchhiker module: 2.5 tons

1x 400L quad adapter: 0.2 tons

1x decoupler: 0.4 tons

= 16.1 tons

Some monopro? did you use all the monoprop before discarding the stage? make sure you have the monoprop drain from the stage you discard first

You upper stage has:

1x 2 person landercan: 2.5 tons (2.66 full of monoprop)

1x full 200-16 tank: 9 tons

2(?) x large battery packs: 0.4 tons

4x large landing legs: 0.4 tons

1x large probe core: 0.5 tons

1x poodle: 2 tons

2x monoprop tanks (or is it goo?): 1.5 tons full

Something else, guessing a large reaction wheel? 0.2 tons

parachutes? (WHY?!) I'm guessing 0.6 tons here

2x extendable solar panels: negligible (0.035 tons)

Total: 16.9 tons I'm guessing...

That is more than the weight of the stage you discard... and the stage you discard has over double the Isp. You'll get more dV if you pump some fuel into it, and use the LV-Ns some more...

You want to transfer x tons of fuel into the lower stage,

where:

(16.9-x)/(16.1+ 16.9-x) = 390/800

(16.9-x)/(33-x)= 0.4875

16.9-x = 16.1 -0.4875x

0.8= 0.5125x

X= 1.56

You want to burn about another 1.5 tons of fuel through your lower stage - thats about 135 units of LF, and 165 of Oxidizer.

But you're carrying over 1.2 tons of monoprop...

To maximize dV, you want to use your lowest Isp fuel first... and you can get a max of 260 Isp with the monoprop on that craft (with the O-10 monoprop engines, you can get up to 290)

Use all your monoprop on the lower stage, then decouple (or transfer ~0.2 tons of LF+O to the lower tank, and burn the LV-Ns for a little extra dV).

Then use all the monoprop from the upper stage, and onlly then fire the poodle.

As far as I can tell, the empty weight of your upper stage is about 7.8 tons.

x 8m/s/s... you need 62 kN to have a TWR of 1 when it is empty.... 128 kN when its full

The poodle delivers 220, your TWR is less than 2 at the start of the burn, but it should be adequate.

Keep in mind every second you spec thrusting down costs you about 8 m/s of dV.... and I don't think the little tricks to tweak a bit more dV out of that craft won't get you more than a few seconds.

When it is full, you've got an acceleration of 13.6 m/s/s, when empty: 27.2

Thus if you're orbiting at 1,800 m/s, it should take you about 100 seconds to stop.

Mass ratio: 2.06... 390*ln (2.06)*9.8 = 2,762 m/s

But that is an overestimate... as its assuming your monoprop fuel is getting 390 Isp.

This is cutting it pretty close on the dV budget, but its doable.

Now for the piloting....as soon as your PE barely touches the ground, place a maneuver node where it intersects the ground. Now drag retrograde all the way back so that you have a burn set to completely cancel your velocity. (I recommend using your low thrust RCS ports for these setup maneuvers, to get that fuel out of the way when a high TWR doesn't matter)

Make a note of the estimated burn time. Divide that by two. If the burn time is 120 seconds, start burning at 60 seconds to the maneuver node.

Assuming constant acceleration (its not, it increases as fuel burns off), your average velocity (since you go from starting velocity to 0) will be half of the velocity that the game is using to compute your time to the maneuver node (you should have placed the maneuver node on the ground, or nearly so), so it will take roughly 2x the time to reach the ground.

Thats why a 120 second burn can be started 60 seconds away from impact (that impact time assumes no burn). As your TWR roughly doubles throughout the burn, it should leave you with a good safety margin. In fact... don't divide by 2... multiply by 0.4... that will result in less dV waste.

That should stop you from smacking into the terrain because you didn't give yourself enough time to decelerate.

Better piloting might save this - it certainly could if you backup to the transfer to tylo, and get a low equatorial PE for the capture burn.

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Holy crap, that's alot of words. Thanks for 'em all. I won't be able to put this info to use until Friday or the weekend, but I did dip into the game to get the exact weights. The weight of the atomic stage with the lander on top, at it's current fuel level: 40.7t. Empty, it's 34.3t. As for the lander, full: 18t, empty: 10t. That's no hitchhiker can, it's a couple smaller fuel tanks. No science things, those are all monoprop tanks. As for the parachutes, this is a multi-use rocket, and I couldn't be bothered to rip them off for this mission.

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The easiest way to land on tylo with that is to crash land...

The easiest way that keeps Mx. Kerman alive is to make it descend, once you are 1,000 m from the surface start burning, if you get to 250 m/s, stop burning and wait until you are at 100 m from the surface, then burn again, if you run out of fuel:

A. Jump out last second, aim so head is down

B. Jetpack land

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Got it--so your dV for the lander is:

dV= Isp * g0 * ln (full/empty)

=390 * 9.81 * ln(18/10)

= 2249 m/s

With the lander on top, and assuming you transfer no fuel, your atomic stage Isp is:

dV= Isp * g0 * ln (full/empty)

= 800 * 9.81 *ln(40.7/34.3)

= 1343 m/s

Intriguing. 2249+ 1343 > 3000 so it's theoretically possible, but you'd have to be a near-perfect pilot. @Kerikbalm is correct: your best chance is to do as much of the burn as possible in the atomic stage at higher Isp. Do what he says and don't forget to rep him!

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Holy crap, that's alot of words. Thanks for 'em all. I won't be able to put this info to use until Friday or the weekend, but I did dip into the game to get the exact weights. The weight of the atomic stage with the lander on top, at it's current fuel level: 40.7t. Empty, it's 34.3t. As for the lander, full: 18t, empty: 10t. That's no hitchhiker can, it's a couple smaller fuel tanks. No science things, those are all monoprop tanks. As for the parachutes, this is a multi-use rocket, and I couldn't be bothered to rip them off for this mission.

Hmmm, 18T for a lander without takeoff capacity nor science : that's heavy. Tylo is quite hard, it required specifically deisigned landers.

For Tylo I desiged 2 landers. One I was quite sure to go there and back : it was a 7 or 8 tons lander with full science and takeoff capacity. The second was a 14T low TWR SSTO, with 6000dv, but I wasn't sure to be able to do it (I succeeded though). Both had a tug left in low orbit of Tylo.

With only 3000dv, you can't do much more than suicid burn and hope for the best, if you have sufficient TWR (which it seems to be ok).

Good luck ;)

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Holy crap, that's alot of words. Thanks for 'em all. I won't be able to put this info to use until Friday or the weekend, but I did dip into the game to get the exact weights. The weight of the atomic stage with the lander on top, at it's current fuel level: 40.7t. Empty, it's 34.3t. As for the lander, full: 18t, empty: 10t. That's no hitchhiker can, it's a couple smaller fuel tanks. No science things, those are all monoprop tanks. As for the parachutes, this is a multi-use rocket, and I couldn't be bothered to rip them off for this mission.

:/

With those more accurate numbers, I'm not sure its worth trying (unless you can go back to a save before you enter tylo's SOI).

I went back and looked at a screenshot I had from my one successful SSTO tylo lander... it got down to the surface of tylo, and then back to orbit (55x60km) with 16 m/s left in the tanks (While it worked, it used a lot of fuel, and I decided its easier to haul new, small landers, than tons and tons of fuel to Tylo, for repeated landings)... anyway, my orbital velocity was 2090 m/s.

I'm sure if I lowered the orbit to be just scraping the mountain tops, it would be over 2100 m/s

Your lander has less than 2249 m/s.

-This is assuming you've emptied the monoprop to find the dry weight, because Kuzzter's calculations assumed everything is at 390 Isp.

Your two cylinder monoprop tanks hold 1.2 tons of monoprop, the capsule, 0.16- > 1.36 tons of monoprop total.

So your lander delta-V would be: 9.82* ( 260ln(18/16.64) + 390 ln (16.64/10) ) = (20.426+ 198.60) *9.82 = 2151 m/s

This means if you lose more than 50 m/s due to gravity drag, you run out of fuel... and you don't have high stength parts that can survive impact speeds of 60 m/s or so...

50 m/s is 6.3 seconds of thrusting against Tylo's gravity.

With the new mass number, it seems your TWR doesn't even exceed 2:1 when full.

18/10 tons full/epty means your initial deceleration will be 12.2 m/s/s and your final acceleration will be 22 m/s/s.

Lets say you average 17 m/s/s.... the burn is going to take you 2100/17 = 123 seconds...

While the start of the burn you'll be thrusting parallel to the surface, by the end, you'll be at a significant angle, and you'll lose more than 50 m/s to gravity drag.

I think you'll probably lose closer to 500 m/s to gravity drag... which is why my initial estimate of 2700 m/s was cutting the dV budget pretty tight.

Now that I know the lander is even heavier... it just can't make it...

That lander simply cannot make the landing on its own, when released even in the lowest possible orbit.... the only way that lander is going to successfully land, is if the stage below it can put it into a very low orbit, and then do a burn to put it at something about 300 m/s under orbital velocity.

From the video, your LV-N stage ran out of fuel before you even got to a low orbit.

Sorry... but this just isn't going to work...

*maybe* if you have an older save, and can do the transfers more efficiently, and arrive at low Tylo orbit with more fuel in your LV-N stage...

But from where you start in your videos.... trying to land is an excercise in futility, it can't be done.

Way too little dV for such a low TWR. If your TWR was infinite, it would still be pretty tight as far as piloting the suicide burn, because... you know... the only 6 seconds of fuel you'd have to fiddle with the throttle and descend assuming you didn't just time the burn perfectly.

*edit*

So I went back and looked at how you arrived at low orbit for Tylo. You start your burnat Perapsis, and lower your apopasis down to just above the surface (somewhat, I'd go lower than 30 km) - turning the old perapsis into the new apopapsis, then you bring your new apoapsis down.

I'm pretty sure that it is much more efficient to start your burn at apoapsis, bring your perapsis down below 30km, then from perapsis, bring your Ap down.

From a highly eliptical orbit, small burns change PE a lot.

This new way- your first burn won't use much fuel at all, and the 2nd burn won't use much more fuel than your first burn from the old way.

Which if that is then used to deorbit your lander before detaching it... could get you annoyingly and frustratingly close to pulling off the landing :P

It takes ~1100 m/s to go from capture to a 10km orbit, or a 10km orbit to escape.

Your first burn is 615 m/s

Your second burn is 530

You use more than this getting into a higher orbit, from well below escape...

It would still be much better if your capture was done with a lower perapsis....

Edited by KerikBalm

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On his last attempts, BenHR was very close : he crashed at 100m/s (IIRC). It may be doable just by optimising the descent.

The main problem is not the vertical velocity, it's the horizontal. You must kill all of it WHILE keeping vertical under control. With high TWR, it's quite easy and efficient : burn rerograde as near as surface as possible (suicide burn) or not so near if you have more fuel. But with low TWR, you can't do it because you loose a lot of time while killing horizontal and your vertical velocity goes uncontrolled. You usually crash in a cliff or ground. You must do a less efficient manoueuver as many described by keeping vertical velocity controled around 100m/s. But this manoeuver is less efficient on delta-V (but more efficeint in survivability).

But as BenHR is so close to land, trying different altitude or selecting higher landing spot or retry manoeuver to burn closer to ground COULD do the trick.

BTW I managed to survive (ship intact and steady) a 30m/s hit on Tylo ground, so vertical velocity can be a bit forgiving. Horizontal is not... if you want to take off later.

Another advice (I think it was already given) : try to burn monoprop first to get to orbit. You can do a lot with RCS. It's just slow and inefficient. But more efficient than keeping the monoprop for the final landing.

Edited by Warzouz

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His last attempt he definitely impacted at over 210 m/s.... Probably about 230 (as he had the kerbal jump moments before impact, the velocity stopped showing, so I'm jsut guessing).

Following retrograd isn't a problem. Its a reverse gravity turn, which is the most efficient way.

That he cut throttle at times is a problem, more gravity drag, shows he was coming in from an orbit athat was too high.

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