CA Mk3 Shuttle - STS-1XL
by gc1ceo
uploaded 2017-09-07
(updated 2018-06-01)
mod ship
#spaceshuttle #shuttle


  • Type: VAB
  • Class: ship
  • Part Count: 62
  • Mods: 3


  • Cormorant Aeronology
  • Squad (stock)
  • TweakScale - Rescale Everything!

MECHJEB Settings

Orbital Altitude: 128 (km)
Prevent Overheats ON
Limit Q to 35000 (pa)
Limit Acceleration to 35 (m/s)
Limit Throttle to 80-100%
Force Roll to -180 / -180
Corrective Steering Gain 2.8

Turn Start Alt 2.5 (km)
Turn Start Velocity 325 (m/s)
Turn End Alt 80 (km)
Final Flight Path Angle 0
Turn Shape 60

History and Background

There were plans for a reusable space planes for as long as the beginning of the dreams of spaceflight. The Space Race between the United States and Soviet Union technically began with the roughest definitions of space planes such as the X-15 which was launched via another aircraft. There were numerous plans for space planes launched from a rocket including the USAF’s Dyna-Soar (cancelled in the early 1960s) and the Soviet MIG-105. However this dream wasn’t realized until the beginning of the Nixon-era program in 1969 that eventually led to development of what became the Space Shuttle. The first orbiter, Enterprise, was finished in 1976 and went through several years of atmospheric tests with first space-capable orbiter, Columbia, finished several years later.

The launch of the Columbia on STS-1 in April 1981 began the lengthy and second-most expensive space program in history which lasted until the final mission of Space Shuttle Atlantis in July 2011. There were 135 space shuttle missions over a 30-year career with two tragic failures which saw the loss of the Challenger on January 28th, 1986 and the loss of Columbia on January 16th, 2003. Both tragedies saw the loss of the entire crews, a total of 14 astronauts. The first couple of missions with Columbia had only two crew with the external fuel tank painted white instead of the orange that became one of its designating features.

Basic Description

The CA Mk3 Shuttle STS-1XL uses primarily Cormorant Aeronology parts and is modified from the original craft made by its author, Pak. It was further adjusted using advice from drtedastro on modifying gimbals, setting up Mechjeb, and making it far easier to fly. I further adjusted it to approximate the earliest configuration of the Columbia during its first two missions including a white external tank. It is designed for short LKO (Low Kerbin Orbits) carrying up to four kerbonauts and minimal payload. The primary mission profile is to use it for training on how to fly the shuttle but it is rated for a payload of up to 10 tonnes and has enough power generated by the fuel cells to stay in orbit for a while.

The 1XL variant specifically replaces the Solid Rocket Boosters (SRBs) with Liquid Rocket Boosters (LRBs) from Cormorant Aernology’s Stage II add-on. This is somewhat grounded in real-life LRB proposals from the late 1980s/early 1990s and once again in the late 1990s. There were several advantages to the LRBs in real life such as increasing crew safety, as LRBs could be shut down at a moment’s notice allowing for safer modes, and greater fuel efficiency in some cases. The LRBs with the 1XL allow for a simpler and more adjustable ascent process as well as, in some cases, a greater payload capacity.

I still highly recommend that most operations are handled through Mechjeb as the craft can be very difficult to control manually, especially during the ascent. I highly recommend a planned orbit between 100 and 130km with drtredastro finding 125-128 km to be the most ideal. The shuttle’s orbital maneuvering engines (OME) are monopropellent with a decent thrust of 100kN but aren’t meant to be used outside of LKO. You should have between 300 and 500 dV upon completing your orbital circularization depending on your circularization procedure. I recommend that you keep 100-130 dV in reserve for your de-orbiting process. There is also a small on-board reserve fuel tank although its primarily meant to be a backup fuel source for the on-board fuel cells.

Launch, Ascent, and Orbital Procedures

The launch and ascent procedure is fairly complex compared to most of my builds, of course this was especially true for the actual Space Shuttle. You should make sure the gimbals for both the Space Shuttle Main Engines (SSME) and Orbital Maneuvering Engines (OME) are locked initially. The LRBs handle a forced roll a bit better than the SRBs so feel free to leave the force roll option on before lift-off. You can also perform the entire ascent with full throttle without the instabilities associated with a full throttle with the SRB variant. The throttle control actually sets all the engines, SSMEs and LRBs, alike so there isn’t a throttle differential like with the SRB version.

The first step, much like in real life, is to fire the SSMEs for just a brief moment while the craft stabilizes on the pad. This is also the chance to initialize the first abort mode, Redundant Set Launch Sequencer (RSLS), which allows you to abort the mission simply by shutting down the SSMEs.

The second step involves firing the liquid fuel boosters, releasing the launch clamps and beginning your lift-off. This is normally where aborting the mission becomes fairly difficult but with the LRBs you have greater control over that difficulty. It is advisable to ride out the booster rockets but it is possible to shut down the LRBs and safely decouple them in an emergency. However if your altitude isn’t sufficient it may extremely dangerous to try and level out before making a landing, but at least with the LRBs it is actually possible. If you keep with the planned ascent then you should keep a straight vertical ascent coupled with a roll so that the top of shuttle is facing your desired inclination. It will wobble some, especially in the few seconds after the lift-off and again during the roll. It is extremely critical not to begin your gravity turn until reaching an altitude of 2.5 km or a velocity of 325 m/s. If you attempt the gravity turn too soon it can fail tragically and cause the craft to topple or flip over.

The third step begins your gravity by freeing the SSME gimbals and locking the LRB gimbals. You’ll probably begin your gravity turn at 2.5km or 325 m/s. You’ll eventually some difficulty once you begin the turn but it’ll probably be a bit smoother than using SRBs. Once the boosters have exhausted themselves this becomes the point where you choose to continue the ascent or begin the second abort mode, Return to Launch Site (RLS) which can be dangerous. Since you are using LRBs with this build you can technically initiate a RLS abort at an earlier point if necessary but it isn’t recommended. The RLS abort mode procedure has to simply eject the boosters and initially continue a somewhat vertical climb. Your RLS procedure will be a bit smoother if you can burn off some of your fuel supply. The difficulty of the RLS abort comes in releasing the external tank and flipping the shuttle around into a landing position. The window for this as a viable option is a bit limited and technically unnecessary in KSP unless you have a SSME failure.

The fourth step,barring a RLS abort, may involve raising your throttle up to about 80% unless it’s already at full. You should keep an eye on your Time to Apogee indicator where you want to avoid letting it dip down below 30 seconds. You also want to make sure it eventually starts climbing up until at least 40-45 seconds. Once you have reached that point you can assume your ascent will be successful. The shuttle may become a bit unstable in varying degrees especially as you move into the upper atmosphere. It should be noticed that most SAS, including while used with Mechjeb, has difficulty handling a set of three engine gimbals. You should avoid trying to address the situation unless you run into a severe problem. You should avoid messing with the gimbals during the ascent or even activating RCS until the ascent is finished.

The fifth step begins when you are near the edge of space and your apogee projection is starting to approach the desired projection. You can stay with 80-100% throttle or reduce it to 40% for a more fuel efficient continuation of the ascent. There is less of a fuel savings with the LRB variants since that part of the ascent is usually more fuel efficient than with the SRB version. Once you have reached space you can initalize an AOA (abort once around) abort using either a single complete orbit or a sub-orbital trajectory. This may become necessary if you have a complete SSME and OME failure. You can often put yourself into a proper orbit with only partial engine function in KSP. The rest of the AOA abort procedure is handled much like a typical re-entry and landing although you may not be able to land at your desired destination.

The sixth step focuses on circularization and can be handled a couple of different ways. However if you added a considerable payload then its very possible your external main tank is already depleted and should be decoupled before circularization. My tests with the LRBs have shown that no matter your ascent throttle process your burn will always be shorter than with the SRBs.
The first method is to abandon your external main tank before circularization and switch entirely to OMEs. It is true that the OME thrust is considerably less than the SSMEs and the circularization burn will deplete your monopropellent fuel supply considerably. However a circularization burn with the OMEs is much easier to control and fix mid-burn because the external tank has already been jettisoned.
The second method, if possible, is to use the SSMEs for the entire circularization burn. The engines have more powerful thrust than the OMEs and this method avoids using your monopropellent fuel supply (except for RCS). It has the disadvantage of leaving the external tank in orbit as debris. This is also not possible if your external tank has already been depleted during the ascent because of increased payload.
The third method, used in real life, is to use the SSMEs for first part of the burn and then switching mid-burn to your OMEs. This is a bit more complicated and requires you to decouple the external tank at the right time to avoid impacting in a significant way with the shuttle. It is recommended that you make the switch somewhere between a perigee of 20-60km to maximize this method’s benefits. The biggest benefits from this method are matching the real-life procedure and having 100-200 more dV available for your orbital operations. You can also add a second OME burn to make further adjustments which mirrors the procedures of some of the Space Shuttle flights.

This also gives you the option for the last abort mode, ATO (Abort to Orbit), due to an insufficient burn to reach your desired orbit but enough to reach a stable orbit (anything above 69km). This may have an effect on your planned mission but it is the safest of all abort modes and was even performed on STS-93 when one of their engines under-performed during the ascent process.

Additional Description and Details

The STS-1X build is intentionally limited so your mission options aside from shuttle training and testing are a bit sparse. However the shuttle bay is very large and can be sealed to allow for safe(ish) EVA training. It has an airlock module much like the actual Space Shuttle which can independently house two crew for both easy egress and even to bring back two stranded kerbonauts. The fuel supplies should let you stay in orbit for about 30 orbits although rendezvous and docking operations can be very challenging. I have added a couple of lights to illuminate the cargo bay so it could be used night-side. There are also several fuel cells and a small fuel tank to handle recharging your electric systems. The primary fuel cells are assigned to an action key, there is also a secondary fuel cell in the rear of the cargo bay that can be activated manually. The secondary fuel cell shouldn’t be necessary under normal operations but has been included in case one of the primary cells are destroyed in a collision. The normal landing procedures require you to have enough electric charge to keep the SAS and lights active, although it is possible in theory to land in one piece without electricity.

Since this is a space place it is meant to land on the runway at the KSC although it is sturdy to make landings almost anywhere on Kerbal including emergency sea landings. The OMEs should be used to de-orbit the shuttle and afterwards should be shutoff and locked since they haven’t much of an effect in the atmosphere. The initial re-entry should be handled with a 40 degree angle of attack to allow the shuttle’s thermal underside to make the full atmospheric impact. You should keep SAS on during the entire trip and make gentle adjustments until you reach 30-40km. Once you have reached this point you should activate all your control surfaces and possibly make a series of broad S-turns to bleed off speed down to about 1000-1200 m/s so that the shuttle is controllable.

Once you hit 30-40km this is where it becomes a true space plane and can be, sometimes not so gently, glided down with control surfaces able to slow it down to around 200 m/s. It can be very difficult to land successfully at the KSC runway but the shuttle can take considerable punishment during the landing. You obviously want to extend the landing wheels probably around 1-2km and unlike real-life they can also be retracted but if you want to stay semi-realistic you should act like they can’t. When you are within 40-100m of landing you should pull back a bit to allow the rear wheels to hit the ground first, known as flaring, and gently apply brakes and the shuttle’s drogue chute. A hard landing may result in losing one of the wheels and a really hard landing may involve losing one of your wings.

Built in the VAB in KSP version 1.4.3.

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