KerbalX

Details

• Type: SPH
• Class: ship
• Part Count: 98
• Pure Stock
• KSP: 1.11.0

Mods

• Squad (stock)

The K-300A Heracles is the first in a series of larger-sized space planes (the 300 series) meant for multi-purpose missions including bringing satellites to orbit, rescue missions for stranded keronauts, etc. I also highly recommend the use of Atmospheric Autopilot which will make aircraft operation much easier. It may be rather difficult to fly solely with stock SAS but it is entirely possible.

The Heracles uses two sets of engines which allow is to operate as both a conventional aircraft meant for supersonic and hypersonic speeds at high altitudes and a horizontally launched space plane capable of orbital missions including carrying a deployable payload up to 1.2 tonnes.

The double Whiplash engines allow for hypersonic atmospheric speeds in excess of Mach 4.5 especially at higher altitudes with a service ceiling between 22 and 25 km. Since the engines can be throttled you can certainly operate at lower speeds and altitudes although it’s not designed for efficient travel at lower altitudes or subsonic speeds.

The four NERVA (Nuclear Engine for Rocket Vehicle Application) are engines that are highly efficient in vacuum and are also used in the upper atmosphere for reaching space but should only be engaged for suborbital and orbital missions.

Atmospheric Operation

The Whiplash engines are meant to operate at high supersonic and hypersonic speeds with considerable range even in the upper atmosphere with a service ceiling between 23 and 26 km. They only operate about 260 kN stationary at sea level but go up to a powerful 772 kN at Mach 3 where they operate at their most efficient.

The most efficient parameters for atmospheric flight is an altitude around 20 km and a speed between Mach 3 and 3.5 which requires careful use of the autopilot and throttle. You should avoid trying to exceed this speed at lower altitudes because of the thicker atmosphere and avoid trying to exceed it at higher altitude since it will significantly reduce your thrust and fuel efficiency.

The powerful engines allow for a considerable rate of climb as you head towards your cruising altitude – a 30 degree pitch is recommended until you reach at least 10 km after which you should start to reduce it to a 20 degree pitch then finally a 10 degree pitch before you decide to level off at your cruising altitude.

Suborbital Operation

All takeoffs should operate with the same procedure – the plane should pitch up by itself upon reaching the proper surface speed. You should have SAS always activated or as it will quickly pitch up and potentially get out of control. You should give it a minute before you decide to activate any autopilots or continue your climb.

You should ascent with a 30 degree pitch until you reach about 10 km at which point you should lower your pitch to about 20 degrees until you reach 20 km or your speed goes below Mach 3 at which point you should lower it further to 10 degrees. You should able to reach close to 26 km before you need to make your engine switch but if you find yourself starting to drop too quickly you can switch engines a bit earlier.

The switch to the NERVA engines will result in a considerable drop in thrust to about 208 kN around 22 km so you should make sure you’re at least Mach 3 before switching engines so you have considerable surface speed. You’ll encounter an immediate drop in vertical speed which will also be reflected in the Time to Apoapsis but simply maintain a pitch rate between 5 and 10 degrees.

Once your vertical speed starts to pick back up you can increase your pitch rate again since with a suborbital flight you’re interested in reaching space and not circularizing an orbit. Once your TWR (thrust-to-weight ratio) reaches about 1.0 you should be able to hit space with ease. If you find your Time to Apoapsis getting too low you might lower your angle-of-attack a bit to as low as 5 degrees until it starts to pick back up.

You should keep in mind that a flatter trajectory will afford you more re-entry time and a shallower re-entry while a more ballistic trajectory will result in a higher altitude but a much steeper re-entry and possibly making your landing more difficult.

Orbital Operation

The takeoff and atmospheric ascent for orbital flight is about the same as suborbital missions with the changes mostly being after you switch to the NERVA engines. Once you have switched to the NERVA engines you should stay with a pitch rate between 5 and 10 degrees until you have passed a TWR of 1.0 after which you can probably just point to prograde until your estimated apoapsis sits around 75 to 90 km. You’ll spend a lot of time in the atmosphere compared to a high TWR rocket so give yourself a wide margin since you’ll incur considerable losses due to atmospheric drag once you start your coasting phase.

Once you have reached space you’ll probably have between 200 and 250 dV although if you have been really efficient in your ascent you might have a bit more than that. You’ll probably need about 100 dV to stabilize your orbit. I recommend reaching a stable orbit first then making adjustments your orbit after that point as needed. You should at least 100 dV left for your orbital mission and your re-entry burn.

This is a multi-purpose space plane so I’ve included a shielded docking port, small cargo bay, and RCS thrusters with a decent amount of monopropellent. It has decent batteries and a number of solar panels so you shouldn’t get stranded on account of lack of electricity. You should keep a small fuel reserve for your re-entry burn but it’s entirely possible to use the RCS thrusters for that in a crunch.

Lastly you might try and keep a small fuel reserve if you’d like to operate the Whiplash engines below 26 km but this isn’t strictly necessary for your re-entry, approach or landing.

Re-entry, approach and landing

Your re-entry burn should be as precise as possible if you want to approach and land on one of the runways – certain addons may aid with that although space plane landings can be difficult for many players. How you handle your re-entry and approach will also have a considerable effect on where you can touch down – the Whiplashes might be somewhat useful if you have saved some fuel.

You should attempt to keep an AoA of between 30 and 60 degrees in the upper atmosphere so you can bleed off speed although the Heracles is fairly stable during re-entry so you can attempt to make some wide s-turns to help with that. You want to still have at least a surface speed between 100 and 200 m/s as you begin your approach so you can make corrective turns and small climbs as necessary.

If you are making an entirely unpowered glide during your re-entry and approach then keep in mind you want to get down to 800 m/s by the time you hit 20 km and sit around 200 m/s once you hit 10 km and about 40 km from your intended landing location. If you are more than 40 km from intended location you probably won’t be able to reach it unpowered.

If you reserve some fuel for powered flight this gives you some leeway and can effectively double or even triple the range of your landing depending on how much fuel and how conservative you are with the throttle. You should keep in mind that the Whiplash engines aren’t very efficient at subsonic speeds so using them might be of limited value.

The considerable lift of the Heracles wings should let you float down pretty smoothly and want to be slower than 60 m/s as you make your touchdown, if it’ll be a rough landing you improve your chances of survival with an even lower touchdown speed. If you have managed to make it to a runway then remember to slightly flare up so your back wheels touch the ground first to avoid a violent wheel barrowing.

Built in the SPH in KSP version 1.11.0.