Reusable Rocketry

[Omni122]

Hey folks,

Sorry if this isn’t the right place to put this, I’m new. Tonight I am going to endeavor into creating a fully reusable launch vehicle. I’ve never been very good at doing reusable stuff, so I was wondering if you guys had any tips! Thanks in advance.

[bewing]

Without mods, it's really difficult to do in KSP -- unless your reusable launch vehicle can get your payload all the way to orbit, SSTO. Stock KSP is really only able to model one craft in the atmosphere at a time.

(That's actually an oversimplification. KSP has something called a "physics bubble" that is a sphere a little over 20km radius, centered on your current craft. Anything inside the physics bubble is modeled. Anything outside is treated as being on a suborbital ballistic trajectory, and when it gets below 25 km altitude, it gets auto-deleted.)

So, if you are controlling a craft in the atmosphere, generally you can't switch control away from that craft. You have to either fly it until it reaches space, or until it lands.

Generally what that means for reusable launch vehicles is that you get your craft and payload on suborbital trajectories and then separate them. Then your payload needs to do a circularization burn, and you need to land your launch vehicle. Sadly, you almost always need to do both of those things at the same time, and you can't. Once your launch vehicle reenters the atmosphere, and you switch control to it so that you can land it, you are stuck flying it until you land. If you wait too long to control it, it will either burn up in the atmosphere or it will fall below 25km and get auto-deleted. Atmospheric drag will not be modeled unless you are controlling the craft.

If you want to use mods, then something like FMRS will help you.

If your launch vehicle is an SSTO, then you can separate your payload at your leisure, and reenter and land the launch vehicle whenever you like.

 

[RP1IsSuperior]

it's a little weird because of the way KSP works. You basically are limited to 2 stage designs. You want to fly a steeper ascent profile than you normally would. You also should have a high thrust upper stage so you can get into orbit fast enough to switch to the  bottom stage and then activate parachutes. If you wanna do a boostback burn, ignite your second stage engine and let it go, do your boostback burn, switch back to your upper stage and go into a parking orbit(just get into a stable orbit, you can fix it later) then switch back to your first stage. I recommend watching Kerbal Space Command's video on this. https://www.youtube.com/watch?v=zFnl4KXfkp0

 

[Serenity]

On 10/12/2020 at 1:25 AM, Omni122 said:

Hey folks,

Sorry if this isn’t the right place to put this, I’m new. Tonight I am going to endeavor into creating a fully reusable launch vehicle. I’ve never been very good at doing reusable stuff, so I was wondering if you guys had any tips! Thanks in advance.

Actually reusability is a lot more feasible than most people think and with good Delta-V Payloads

Here is how i think its the best way to do it without mods,

Launch a two-stage rocket, raise your apoapsis to 100-110k with a semi-aggressive gravity burn and then immediately separate the stages,

Switch to second stage and start an aggressive circularization burn, the goal is to reach Periapsis 70k as fast as possible, before the first stage goes into atmosphere(its very doable).

After you reach orbit with the second stage, switch to First Stage.

Now you have two options, you can try to burn back from where you launched or do a ballistic land close to where you heading.

Eitherway you gonna waste a lot of fuel.

Remember to put 3-4 airbrakes, do a few burns to slow down etc.

After you reach kinda close to the ground, burn and hover your rocket, zeroing every vertical and horizontal speed

keeping the SAS locked to retrograde, when you reach close to zero speed press F to quickly toggle SAS and that lifts the lock to retro.

then let it go and burn again close to ground, just waste the fuel to keep that tricky horizontal speed to zero.

To land i recommend https://forum.kerbalspaceprogram.com/index.php?/topic/195546-110-kre-kerbal-reusability-expansion/ for landing legs.

Or else you can land on your engines but you need to be on very flat terrains.

Here is one of my ''old'' builds, full stock except those shiny landing legs.

First Stage only, the second stage can vary, and it can take huge 2nd stages(Even a sizeable shuttle etc) and many tons payloads:

https://imgur.com/MWVglVd

 

 

Edited October 14, 2020 by Boyster

[Wobbly Av8r]

17 hours ago, Omni122 said:

Hey folks,

Sorry if this isn’t the right place to put this, I’m new. Tonight I am going to endeavor into creating a fully reusable launch vehicle. I’ve never been very good at doing reusable stuff, so I was wondering if you guys had any tips! Thanks in advance.

Great ideas and information already from the posters above, so I'd only want to add some other thoughts on the matter...

While I believe SSTO's to be the hands-down winner of the reusability contest, they can be a 'handful' to operate successfully... repeatedly through recovery... with differing size and weight payloads. And most importantly they lack the majesty and projection of sheer power that accompanies a full-on Rocket Launch (tm) !!! So what I guess I'm trying to say is that there are a number of ways to skin this cat (no cats are/were harmed in the making of my Kerbal Space program).

As an example of a compromise, my favorite is a core reusable booster that can be supplemented with various SRB's (unfortunately -but necessarily- disposable) to accomplish placing various payloads into LKO - for instance, I can place 18 tons into LKO for a total cost of less than 7,000 kerbucks, and using SRB's, place 42 tons into LKO for less than 21,000 kerbucks. De-orbiting the booster can be done 'at my leisure' which enables me to not only deal with the primary payload's trajectory in a timely manner, but also allows me to maximize recovery costs by de-orbiting such that touchdown is close to KSC. And this type of reusability demands much lower 'maintenance' than dealing with an SSTO. (While I love the idea of @Boyster landing the booster back at KSC similar to Space-X's ventures, it would require much of the 'maintenance' of an SSTO to recover accurately, while the ability to toss out a couple of 'chutes and not be choosy about whether you'll be on land or water near KSC is worth the trade-off to me...)

Just food for thought.

[jimmymcgoochie]

If you want an easy way of recovering dropped rocket stages, there are a few mods that can do that. My personal favourite of those is Stage Recovery as it's simple (slap some parachutes on, or a control point and extra fuel for a powered landing when the rocket is too big for chutes) but also very configurable (you can change the min/max speed for recovery, % of the value returned depending on distance, speed, risk of stages 'burning up' before recovery and more) and requires no in-flight input- just drop the stages with enough parachutes or some reserve fuel and a probe core and the mod will detect when something drops below the 'death zone' of ~25km and recover it for you. It even works with crewed vessels and science experiments/data stored on board.

It's feasible, but very difficult to do a 'proper' recovery with a rocket and requires either an inefficient launch profile, which wastes quite a bit of fuel, or a landing some distance away from the KSC, which gets less funds from recovery. There is another way, however- build a single stage to orbit (SSTO) rocket that can reach orbit on its own, deploy a payload and then re-enter to land at/near the KSC; the 'Twin Boar' engine is particularly good for this as it has an unusually high impact tolerance of 20m/s, meaning you can drop it pretty hard and it won't explode (which saves mass and drag from landing legs) plus it's a powerful engine with built-in fuel and a pretty reasonable cost making it an economical choice too.

When you see SSTO, it's usually referring to a plane rather than a rocket and spaceplanes are definitely an option worth pursuing to carry payloads into orbit for minimum costs- unlike a rocket which has to fight directly against gravity with thrust, a plane can use aerodynamic lift during the ascent meaning it can carry more mass and needs less thrust; there's also the bonus of using a combination of air-breathing engines (which are much more efficient than any rocket) and the NERV nuclear rocket engine (most efficient stock rocket engine) which both run on liquid fuel without the need for oxidiser, saving mass which is always a good thing.

If you're looking for a good SSTO for a career game, I recommend this one- requires only level 2 facilities, cheap to operate, can carry 20 tons or more into low Kerbin orbit (LKO) and flies well both with and without a payload attached making it a great workhorse.

https://kerbalx.com/Kronus_Aerospace/Kronus-LowTech-20-Ton-SSTO

There's also this pretty simple SSTO rocket which apparently has a similar payload capacity and can be easily recovered using the sturdiness of the Twin Boar to save on parachute mass, although I haven't been able to make it work myself (probably due to too many mods in all my games ):

 

[king of nowhere]

the most comfortable way to reuse rockets is to send a big enough rocket to enter orbit with a single stage. then you detach the payload, deorbit the rocket, and recover it.

I developed this launcher that's the best I can do for money effectiveness. with a payload fairing and a good trajectory, it can bring 25 tons in orbit, at a net cost (considering to recycle the rocket) of around 11k kerbodollars, slightly less than 500 per ton of payload.

 

 

[BigStar Aerospace]

I know this thread is a bit old, but recently I've been delving into reusable SRB core stages for my new career mode which is the hardest one yet. I use a very steep launch trajectory while using the first stage to get an apoapsis of at least 100 Km, then an  efficient upper stage that can push the payloads apoapsis as far away as possible while keeping it the same altitude. Then once the apoapsis is at a MINIMUM of 10 minutes away, then I switch over to the booster. What I've done (I use DLC) since I don't have airbrakes is use the robotic parts, specifically the small alligator hinge as well as a square wing piece and a KALL-1000 Kontroller to deploy the airbrakes, I can explain the airbrakes more if needed. And then at the bottom of the large SRB, I'll have either Shrimp or Mite engines pointing upwards for when the SRB reaches apoapsis, if you're in career mode, you want the stage to land as close to the KSC as possible to get the most funds recovered as possible. After those are fired at apoapsis and the airbrakes are deployed before I reenter the atmosphere, I point prograde with the heatshield on top of the booster ensuring that minimal damage occurs during reentry.  Then once I get down to 12 Km and I'm going slow enough, I deploy the drogue chutes at 5 Km, then I slowly descend to 2.5 Km to deploy the main chutes, the amount of these needed depends on the boosters weight, I use six for the Clydesdale and 4 for the Thoroughbred. You also want enough reaction wheels in the booster so that when you splash down you can hold radial in to ensure that the booster doesn't tip over and ruin some of the technology, this can also be done by adding weight to the top of the booster so it always wants to face down, this wastes fuel, but is more realistic. Then once it's below 0.3 m/s I recover it. Similar techniques can be used with liquid fuel boosters, all though the extra parts can cause some noticeable differences.