Stock part Nara mission (JNSQ)

[Leganeski]

Part 0: Introduction, concept, and design

 

When I first looked the JNSQ delta-v map, I was intrigued by the "ruby slippers" icon on Nara.  Some research revealed that it meant "returning from the surface is impossible." This seemed like a rather bold claim, until I found that Nara's atmosphere had a surface pressure of 40 atmospheres: at that pressure, rocket engines do not produce any thrust.

Despite this, returning to orbit from Nara's surface to orbit has been done before, using Explodium Breathing Engines. This is absolutely the correct way to properly take advantage of the hydrogen in Nara's atmosphere. It doesn't disprove the claim on the delta-v map, though: JNSQ is designed for balance with stock parts, so the numbers on the map should reflect the requirements without part mods.

However, Explodium Breathing Engines aren't the only way to produce thrust on the surface of Nara: propellers work very well at the high atmospheric densities found there.

This led to an idea: Why not use propellers to simply lift a rocket to an altitude with a more reasonable pressure? This would avoid part mods entirely.

It's not a new idea, and has been successfully performed on stock Eve, a planet with a comparable atmosphere. There have even been discussions about adapting the design for Nara, but as far as I can tell, nobody has actually done it yet.

I built a craft to test the concept, and it got off the ground just fine. Then it immediately flipped over and crashed.

After a lot of testing and a lot of spinning out of control, I finally realized that the problem is exactly what control surfaces are for. After adding adjustable fins, the very next test was successful.

I wasn't sure what to call my new craft: it's not a helicopter because it uses control surfaces to steer, but it's not a plane because it doesn't have wings. Eventually, I gave up and called it the Nara Ascent Vehicle.

The Nara Ascent Vehicle prior to ascent.

It uses four EM-32 rotors, each with eight R-12 ducted fan blades (used instead of normal propeller blades so that they won't hit anything). The two diagonal pairs of rotors rotate in opposite directions, cancelling out the overall torque. They are mounted at the bottom so that they can be removed with a standard small decoupler without needing any heavy structural parts. The landing gear and fins are attached with separate decouplers, mainly so that the fins can stabilize the rocket as it jettisons the propellers before being jettisoned themselves. 

Nara is so far away from the Sun that solar panels produce virtually no power. Instead, 16 RTGs are stored in two service bays below the central rocket stack. They are jettisoned along with the propellers.

I don't remember the exact total mass of the rocket helicopter plane vehicle after it landed on Nara, but it was less than 30 tons including the descent equipment (which was detached before the point shown in the picture).

 

Now, I needed to get the vehicle to the surface of Nara.

 

 

Part 1: Getting to Nara

 

The initial rocket on the launchpad.

The mission begins on the launchpad. Inside the fairing is the Nara Ascent Vehicle and a nuclear stage for interplanetary travel.

The mission begins 36 seconds after the start of the save file, which in JNSQ is at 06:00:00 on day 1.

I used KSP 1.12.3, with Making History and Breaking Ground.

The only mods I used were JNSQ itself, and BetterTimeWarpContinued to get to Nara in a reasonable amount of time.

The mission was performed in Sandbox mode with Normal difficulty settings, including CommNet. However, it only used pilots for control and didn't transmit any data, so no communication was required.

 

Spoiler

The Nara Ascent Vehicle, on the right, is inside another fairing to protect it during the descent to Nara's surface.

 

 

The maneuver node for the transfer to Nara. The burn time is long, but at 2.5x scale, it's not as much of an issue.

 

The burn starts with the remaining fuel in the chemical stage.

 

Continuing the burn with the nuclear stage. The rocket dips slightly into the atmosphere, but not enough to produce any effect.

 

The result of the burn. It's not quite an encounter (Nara's SOI radius is 20.21 Gm), but it's close enough for the Kerbin ejection.

 

Leaving Kerbin.

 

After some course corrections, the rocket achieves an encounter with Nara.

 

The rocket arrives at Nara and begins the capture burn. Nara is huge, so the rocket captures easily.

 

The apoapsis is kept far away, making the plane change burn there very cheap. Nara rotates at 523 m/s at the equator, so deorbiting from a prograde orbit will significantly reduce the speed relative to the atmosphere and decrease heating.

 

Even the 10-meter heat shields can't survive deorbiting the Nara Ascent Vehicle from a surface speed of 7500 m/s, so the orbit is circularized before descent.

 

The nuclear boosters are decoupled.

 

The nuclear stage doesn't have great TWR, so the circularization burn is split up.

The Nara Ascent Vehicle is now in low Nara orbit, and prepares to descend to the surface.

 

Part 2: Reaching the surface

The Nara Ascent Vehicle deorbits wrapped in a fairing and two heat shields for thermal protection.

Spoiler

The top heat shield is inflated to provide stabilization during descent.

 

The deorbit burn begins.

 

The burn continues well into the atmosphere. At this point, the nuclear stage is close to exploding, and must be jettisoned despite the remaining fuel.

 

The front heat shield is inflated for additional protection. Only the reaction wheel is exposed to the air, but it's still almost completely shielded.

 

The heat shield gets quite hot, but survives comfortably.

 

After slowing down, the rear heat shield is jettisoned.

 

The fairing deploys, revealing the Nara Ascent Vehicle.

 

When the craft gains enough control to flip, the rear heat shield and reaction wheel are decoupled. The throttle is currently mapped to the torque limit on the rotors, so it is increased to prevent them from spinning.

 

The craft is turned prograde to speed up the long descent.

 

As the surface gets close, the craft turns to the side to slow down to a safe speed.

 

The parachutes can now be deployed.

 

At 100 meters above the surface, the parachutes deploy fully.

 

Four parachutes are complete overkill for Nara's ridiculously dense atmosphere.

 

Landed safely on the surface. The pressure here is 33.61 atmospheres, and the air is about 20 times as dense as Kerbin's at sea level.

 

Jeb cannot get out to plant a flag, so he instead takes an EVA report from the surface.

Part 3: Getting back to orbit

The Nara Ascent Vehicle performs its task.

 

Spoiler

The parachutes are jettisoned and the rotor torque is set to the maximum.

 

The propellers begin to lift the craft off the ground.

The fins quickly stabilize the craft.

 

The propellers spin at full power, increasing the speed to the point that an enormous amount of drag is created. However, with RTG power and fins for stabilization, this isn't really a problem.

 

The power supply isn't unlimited, though, and the torque limit is decreased to conserve electricity somewhat.

 

The ambient pressure has now fallen to 20 atm.

 

The ambient pressure reaches 10 atm.

 

The ambient pressure reaches 5 atm. The craft continues to accelerate.

 

The ambient pressure reaches 2 atm. The craft is still accelerating, but only barely.

 

The rotors reach their maximum RPM. The propellers now start to produce less and less lift, and the craft starts to slow down. However, it can continue ascending for some time longer.

 

The ambient pressure reaches 1 atm. The angle of attack of the propellers is decreased to maintain lift.

 

At this point, the ambient pressure is 0.88 atm. The propellers can no longer provide enough lift to maintain the ascent, and are jettisoned. The rocket engines activate. At this pressure, the central Reliant and outer Sparks provide plenty of thrust.

The atmospheric density here is only about half of that at sea level on Kerbin, so drag is not too much of an issue either. However, it cannot be ignored, and the upper fairing remains on.

 

After the rocket stabilizes, the fins are no longer necessary, and are jettisoned.

 

The rocket begins the gravity turn.

 

The boosters run out of fuel and are detached.

 

The Reliant continues burning.

 

The Reliant finishes burning.

 

The fairing is deployed and the Spark stage ignites. 

 

The TWR of this stage is not great, so the rocket turns up slightly from prograde.

At this point, the rocket is in space and just needs to circularize its orbit.

As TWR and centrifugal force increase, the rocket returns to prograde.

 

The final stage, powered by four Ants, ignites.

 

The circularization maneuver.

 

The rocket reaches a stable orbit!

 

The rocket finishes circularizing.

The trip from Nara's surface to orbit is not impossible after all, even with stock parts!

The amount of delta-v used is hard to calculate, because the hard part of the ascent relied on propellers, which are not reaction engines and don't satisfy the rocket equation. However, the rocket stages used about 7000 m/s (at the initial ambient pressure of each stage; the vacuum value is somewhat higher). This is certainly a lot, but not an impossible amount.

 

Part 4: Return to Kerbin

 

The Nara Ascent Vehicle has 1043 m/s of delta-v left. A direct burn to a Kerbin encounter would take about 2500 m/s at minimum, which I don't have. However, gravity assists can significantly reduce this.

The easiest celestial body to get an encounter with from low Nara orbit is Amos, Nara's first moon. From my orbit at an altitude of 267 km, I need a burn of only ... 2108 m/s.

Well, I guess that isn't going to work.

 

Part 4: Rendezvous with the Nara Ascent Vehicle

Thankfully, I have another pilot.

Valentina gets in the Nara Return Vehicle. This one actually is a rocket, but I wanted its name to be consistent with the Nara Ascent Vehicle.

Spoiler

The Nara Return Vehicle has over 19000 m/s of vacuum delta-v. I wasn't sure exactly how much fuel I would need, but this is sandbox mode, so I took the "MOAR BOOSTERS" approach.

 

 

I don't have as much TWR this time, so the maneuver only goes to Jool, which will provide a gravity assist.

 

Starting the ejection burn.

 

Activating the nuclear stage.

The rocket dips down into the atmosphere to maximize as much of the Oberth effect as it can. Although the rocket is starting to heat up, this is mainly due to the high speed through the atmosphere, and the actual drag force is very minor.

 

The rocket safely escapes the atmosphere.

 

The first set of fuel tanks, now empty, is jettisoned.

 

After some more burning, the second set of tanks has been used up.

 

Due to Oberth losses, the burn continues after the next set of tanks runs dry.

 

The Jool assist also puts our ascending node in precisely the right spot.

 

The Jool assist. The gray speck that my mouse is pointing at is Tylo.

 

This gray speck is Laythe. I couldn't find Vall, probably because it isn't big enough to see from this distance.

 

After some period adjustment at solar periapsis, Val gets a Nara encounter.

 

The adjusted encounter.

 

Capturing at Nara.

 

As before, the plane change is very cheap.

 

Val begins circularization to match orbits with Jeb.

 

Another set of fuel tanks is dropped.

 

The main boosters finally run out of fuel and are jettisoned. The center engine continues circularization.

 

Jeb comes into view. The Nara Ascent Vehicle at this point is mainly just him and two Oscar-B fuel tanks, so it appears very small even from this close.

 

Rendezvous is completed. Jeb's helmet can be seen more clearly.

 

Jeb easily finds the Nara Return Vehicle, which is much bigger in comparison.

 

Jeb gets out of his chair, puts the EVA report in Val's command pod, and gets inside the Nara Return Vehicle, if you can call a chair in a service bay "inside".

 

Part 5: Return to Kerbin

Jeb has now joined the Nara Return Vehicle, which prepares to go back to Kerbin.

Spoiler

Leaving Nara will result in a heavily inclined orbit. However, a Lindor assist will cheaply fix the inclination.

 

The ejection burn begins. A nine minute burn would normally be bad, but Nara's density is low enough that it's not a problem.

 

The next pair of fuel tanks is discarded.

 

The burn is completed, and ... there's no Lindor encounter. This is going to take a long time to fix.

 

By "a long time", I mean about 700 years. This is beyond the range of the default Better Time Warp settings, so I create a new one.

 

Eventually, a Lindor approach is achieved.

 

The Lindor assist. The speck that my mouse is pointing at is ... uh ... Aden? I think it's Aden. It's definitely one of Lindor's moons, but I'm not completely sure which one.

 

There's another moon on the right edge of the screen. It's probably Huygen.

 

The result of the Lindor assist. My orbit is much better, but it's not quite all the way to Kerbin.

 

I decide to simply decrease my periapsis to intersect Kerbin's orbit. It's somewhat expensive, but I have a lot of extra delta-v.

 

The Kerbin encounter. It's above the atmosphere in case aerobraking fails.

 

The rocket burns retrograde to set up the aerobraking attempt and also decrease its speed relative to Kerbin.

 

The remaining fuel is no longer needed.

 

The capsule enters the atmosphere at 7283 m/s.

 

The re-entry heating is significant, but nothing an oversized heat shield can't handle.

 

The capsule reaches periapsis. However, it has already been successfully captured by Kerbin.

 

The heat shield runs out of ablator. However, it has slowed down enough that it doesn't burn up.

 

The capsule reaches apoapsis and begins to descend again.

 

The re-entry effects diminish as the capsule loses speed. However, the drag forces are still high.

 

The parachute is released.

 

The parachute deploys.

 

The heat shield is jettisoned to reduce mass, and the service bay doors opened to increase drag.

 

The capsule lands safely on the surface.

 

The end result of the mission: an EVA report from Nara's surface, returned safely to the surface of Kerbin, without any part mods.

 

This mission was not optimized much at all: there were significant margins between every section. During the mission of the Nara Ascent Vehicle, I could have saved ~2300-2400 m/s by taking a Kerbin-Eve-Kerbin-Kerbin-Jool-Lindor-Nara route, 1150 m/s by aerobraking from a Nara periapsis of 140 km (as I had done successfully in my tests), and 1928 m/s in fuel that I jettisoned or had left over when Jeb transferred between the crafts. The Nara Return Vehicle also simply jettisoned its last 3695 m/s of fuel. And all of that was with my noticeably imperfect piloting skills (which can be seen in the video of the ascent).

This goes to show that a round-trip Nara mission is not only possible, but comfortably within the range of feasibility even without any part mods.

 

Craft files:

Nara Ascent Vehicle

Nara Return Vehicle

[Autochrome]

Impressive! I thought it couldn't be done with stock parts, but I guess I was wrong. Now I can finally be saved from Nara (Read my location).

[jimmymcgoochie]

Bravo!

It can be done after all, and without resorting to cheating mods.