KerbalX

Description

A stock aircraft called fulgur-Wisp2b. Built in the SPH in KSP version 1.6.1, with 74 of the finest parts, its root part is mk2DroneCore.

Details

• Type: SPH
• Class: aircraft
• Part Count: 74
• Pure Stock

Summary

Alternative design for the original Wisp 2 by fulgur, in response to his request for assistance.
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KCSS SSTO - brings 6 kerbals + 3t supplies to 120km orbit and back with 5% margin,
using 10 parts, 10k funds, and 11t less than the original.

Mods

• Squad (stock)

Rationale

fulgur was having limited success getting his Wisp 2 SSTO up to the 120km target orbit of the KCSS, and asked for tweaking assistance.
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A test flight of the original showed several large sources of drag:

• the LES attachment point, a ‘hidden’ Mk2-Mk1-Mk2 transition without adapters
• many drag-exposed surface-attached parts required by the LES and RCS subsystems
• zero angle-of-incidence on the wings, keeping the Mk2 main body considerably off prograde during most of the ascent

Additionally there were extra Mk0 and Mk1 pods adding cost and mass due to the fuel-hungry engine assembly.
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The alternative design incorporates the following improvements:

• an additional offset Mk1-Mk2 fuel adapter is added to remove the main drag-inducing Mk1-Mk2 transition
• moving LES-required surface-attached parts into the cargo bay
• replacing the very draggy RCS thruster blocks by a minimal use of linear RCS ports centered on orbital CoM
• slight offset adjustment to properly shield the forward ‘supply containers’ (ore tanks) inside the cargo bay
• 5 degrees of angle-of-incidence on the fixed lifting surfaces to allow the Mk2 body to remain close to prograde in flight
• a good bit of additional lift, helping to keep the craft close to prograde during most of the ascent
• removed no longer required Mk0 and Mk1 pods and reduced engine count
• re-added the science container that was somehow lost from the first iteration fulgur posted

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The Wisp 2b uses 2 engines, 10 parts, 10k funds, and 11t less total mass to lift the same 6 kerbals and 3t of supplies to the intended 120km KCSS orbit, while keeping a 5% fuel margin for contingencies, and still maintaining most of fulgur’s original design features.
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Note: This is just a design suggestion; fulgur has full permission to finalize this design and repost the finished craft.

Usage

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Ascent (to 120km equatorial orbit)

• engage brakes and SAS, set throttle to 100%
• (helpful: set target to Mun or other orbiting body when at 7.5 degrees over horizon)
• release brakes and stage jets
• at 60 m/s pitch to 7.5 degrees (or switch SAS to target mode, to avoid manual input)
• at 14km altitude, stage the aerospike
• at 45km altitude, set SAS to prograde mode
• cut throttle when Ap reaches 122.5km altitude
• typically, there will be a 0.1 degree inclination - at AN, burn minimal throttle to anti-normal to correct
• circularize at Ap (60-65 m/s, 6s burn)

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Descent (from 120km equatorial orbit)

• exactly opposite of KSC, burn 80 m/s retrograde
• deactivate aerospike, engages brakes and activate jets
• reenter atmosphere on SAS radial out
• when nose starts lowering by itself, set SAS to stabilize
• craft will settle in stable +10 degree pitch above prograde
• release/engage airbrakes as needed to stay on target (will stay engaged most of the way)
• release airbrakes when dropping subsonic
• (helpful: deactivate roll control on one of the elevon pairs to make it less touchy during landing approach)
• if somewhat off target, there should be enough LF to throttle up for a controlled flight approach

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Launch Escape System

• <40m/s: hit Abort and let pod roll to a safe distance before staging chutes (*) and brakes
• 40-60m/s: critical window. Requires more immediate interaction, as the pod will hop off the runway but the gained altitude and glide time will be limited. Hit Abort and pitch up for a controlled glide while quickly staging the chutes (*)
• >60m/s: hit Abort and let pod glide a safe distance away, glide to water landing or stage chutes (*) over land
• suborbital: hit Abort and keep SAS prograde to let pod aerobrake and glide to a water landing or stage chutes (*) over land

(*): note that due to separation from the main craft, staging the pod chutes requires staging twice