Tartarus: Tylo and Back in Alternis Kerbol (Ongoing)

[Beriev]

Hello all.

This thread will be on a mission where I land a kerbal on Tylo in Alternis Kerbol and return them safely to Kerbin. As of writing this initial thread, I've designed, tested, and assembled all the mission hardware and just need to fly it.

Introduction

Alternis Kerbol (modernized as Alternis Kerbol Rekerjiggered) is a mod originally released in 2013. It revamps the solar system to be more challenging, with Tylo having one of the most drastic transformations. The ex-moon is now a standalone world orbiting near where Duna used to (Duna and Dres are now moons of Tylo), and now possesses a radius of 1103 km, a surface gravity of 4 Gs, and a thin, hot atmosphere that makes Eve's look tame.

Online, I've only located two people who have returned kerbals from Tylo  - @metaphor and @Xurkitree. However, metaphor's mission (video here) was accomplished with no aerodynamics or reentry heat, while Xurkitree's mission (video here) tortured his kerbal with 6 years on Tylo's surface in a command seat, and to top it all off, neither included science gear. I am going to change that. I will be landing a kerbal on Tylo with a pressurized pod and full scientific suite, while minimizing time under Tylo's crushing gravity.

Part 0: Craft Overview

This is Tartarus, the single-launch ship I've developed, as it will look in low Kerbin orbit. It's named after the abyss of torment and punishment from Greek mythology, which I found to be an apt description for Tylo, too. The ship weighs around 1715 tons at the start, and has 3 main sections: the command section, the lander, and the transfer stage.

At the top is the command section (which will carry the name Tartarus), which includes the return capsule, the transfer habitat, and 4 satellites. The satellites consist of 3 scanners, which aim to map all bodies in the Tylo system, and 1 relay, which will provide constant communication for the lander while on the surface.

In the middle is the Tylo lander, Bonecruncher. The name was chosen due to the extremely high G-forces sustained during landing and ascent. The high mass, at 769 tons, was due to me opting for a powered descent instead of heat shield spam. The lander carries a full set of scientific instruments and ISRU kit, which I've tested to refill the ascent stages in under 150 kerbin days when landing in an ore-rich spot.

At the bottom is the unnamed transfer stage. It uses vertical asparagus staging to eke out 5 km/s of delta-V while pushing Bonecruncher and Tartarus, which should be enough to get to a 25x25 km orbit around Tylo, while still leaving enough fuel to return home (though if there's insufficient fuel, I'll launch a refueling craft).

Tartarus needs to still get to space, however, which is where this launch vehicle comes in. It is a fairly simple 3 stage setup, each stage primarily using varying quantities of an OTRAG-esque common booster (consisting of two S3-14400 tanks and a Mammoth engine).

Unfortunately, the VAB is too small to show the entire assembled rocket inside of it, so the full image will have to wait for the next part.

Edited December 10, 2021 by Beriev

[Beriev]

Part 1: The Journey to Tylo

As promised, this is Tartarus, fully stacked on the pad. At 9910 tons, it is the most massive stock rocket I've seriously built, but nowhere near my personal record (that one is from this mission). The harsh sunlight is from base Alternis Kerbol, not any ambient light boost in my settings.

Tartarus's launch date was ~Y1 D168, stock Kerbin-time. This mission has three kerbals aboard - Valentina, Bill, and Bob. As is quasi-tradition with these super-duper-heavy launchers, I hand off the reins to MechJeb, who can handle lag much better than me.

The first stage is rather cleanly dropped at 13 km (the explosion is from the decoupler).

The second stage follows suit at 39 km, where it also starts becoming clear the ascent was a little too shallow to be efficient.

One coast, fairing deployment, and circularization burn later, Tartarus attains a 103 km x 100 km low Kerbin orbit. I ballpark the ascent delta-V at ~3.8 km/s.

Shortly after orbit attainment, I window-hunt to find a transfer directly from Kerbin to Tylo. I originally planned to eject into Jool orbit, and then burn to Tylo transfer from there, but this method was efficient enough (0.95 km/s vs. 1.6 km/s) to make it worth the effort, plus giving an opportunity for easier periapsis kicks. Tylo orbits a little beyond Duna's old orbit, hence the longer transfer time, at 1 year.

The last of the fuel from the launcher starts the first kick before the 21 nuclear engines take over (that explosion was the probe core meant to de-orbit the upper stage).

On one of the later kicks (piloted by MechJeb for precision), the first pair of drop tanks is ejected.

Kerbin's gravity well is deep enough that the final kick from an elliptical Kerbin orbit to a Tylo transfer is less than 100 m/s.

Due to Jool's proximity to Kerbol, Tartarus takes only ~15 days to escape its reduced SOI, while the crew settle in for the long haul.

One year (and one ~106 m/s deep-space correction) later, Tartarus plummets towards Tylo. The planet might seem distant, but this image was taken just under an hour before reaching periapsis.

Tylo's deep gravity well makes the elliptical capture pretty cheap, at 120 m/s, although the second pair of tanks are also dropped during this burn.

Now in a 150 Mm x 40 km orbit, it's time for Tartarus to investigate Tylo and its moons via its probes before gearing up for landing.

Edited December 10, 2021 by Beriev

[Beriev]

Part 2: Probes and Circularization

(College has been annoyance for the past five months, putting this mission on hiatus. Now, I am back to finish it.)

While swinging out to apoapsis, the 4 sub-probes eject to explore the Tylo system in-depth. Tartarus will wait an extra orbit while the probes establish their orbits.

The Tylo mapping satellite, TyloScan, is the first probe to arrive at its final orbit. It circularized into a 125 km x 125 km polar orbit to scan for ore.

Next was the Tylo communications satellite, TyloComm, which circularizes into a 15.5 Mm x 15.5 Mm equatorial orbit. Unfortunately, due to Dres's orbital altitude and SOI size, a stationary orbit is impossible (any object in such an orbit will crash into Dres), so TyloComm enters an orbit slightly below the proper altitude.

After that is the Duna mapping satellite, DunaScan, which leverages the moon's thin atmosphere for aerobraking. Similar to TyloScan, it also secures a 125 km x 125 km polar orbit.

Finally, the Dres mapping satellite, DresScan, finishes off the four probes, entering a lower-than-usual 30 km x 30 km polar orbit.

Now with the satellites in place and scanning, the crew on Tartarus search for a valid landing site on Tylo. They are looking for a location with a high ore concentration, low latitude, and low ASL altitude. A site is soon selected, at the bottom of a canyon smothered with impact ejecta from a basin in the northern hemisphere. The map view below shows the landing site and its coordinates, as well as Tartarus's inclined eccentric orbit.

The first order of business is to make Tartarus's orbit equatorial, accomplished using a 13 m/s plane change burn near apoapsis.

Then, after jettisoning the sub-probe adapter to minimize mass, the ship starts circularizing into a very low Tylo orbit, a 2700 m/s burn split into 250 m/s maneuvers to maximize the Oberth effect. During these burns, the third...

...fourth...

...and fifth pairs of drop tanks are ejected...

...along with the pair of nuclear engine clusters (which were dropped on a suborbital trajectory)...

...before Tartarus, at long last, secures a 25 km x 25 km equatorial parking orbit. The burns took about 3000 m/s in total, an overrun of ~11% due to Tylo's nasty gravity losses.

Due to Tylo's distance from Kerbol, the transfer window back home is permanently open, so there's no advantage to lingering in low Tylo orbit. As such, the crew, especially Valentina (since she's piloting Bonecruncher), elect to land as soon as possible.

Edited May 19, 2022 by Beriev