Atmospheric Reentry

Atmospheric reentry is the process by which spacecraft from orbit of a planet or moon enter the atmosphere and reach the planetary surface intact. Typically this process requires special methods to protect against aerodynamic heating. Various advanced technologies have been developed to enable atmospheric reentry and flight at extreme velocities.

Planning an entry

Select the surface destination on the navigation instrument, then open the Orbit MFD's REENTRY. AUTO compares direct powered entry with coasting on the current orbit before entry. HANDOFF selects the requested atmospheric transition time; H ALT and H TAS select its altitude and air-relative speed. The initial test target is 30 km MSL / 0.5 km/s TAS, upstream of the waypoint. It is not a landing point or a universal safe condition.

The automated-entry alpha can execute an ENTRY READY plan from orbit after undocking, using current loaded mass, forward/reverse mains and separate RCS limits. Its preview checks 95% of Vne and 200°C predicted AFT, with thrust, engine-response and attitude margins. These are controller settings to validate, not newly certified vehicle limits. The nose stays into the air-relative direction of travel during reverse braking. Active protection can sacrifice the requested time to brake and arrest descent.

At the achieved atmospheric handoff, DOR sounds its disconnect once and engages altitude, heading and TAS hold. In the newer arrival/FPA alpha, a valid runway FINAL choice aligns the atmospheric handoff with the runway and uses NAV instead of heading hold. The ILS, visual-final and VTOL lines are advisory previews: DOR does not descend to the final gate, arm LOC/G/S, hover or land. FPA is available for pilot-selected atmospheric descent; TAS hold can continue through supported NAV/LOC and vertical-mode changes. Cancel the TAS hold with the DOR control or manual throttle input; disconnecting the aircraft autopilot also cancels it. The pilot remains responsible for ATC routing, terrain, descent and approach. The model does not forecast changing weather or terrain clearance.

Client version matters: earlier calibration clients say REENTRY PLAN / PLAN ONLY and do not execute entry. They can still record a manual entry with REC. In the automated-entry alpha, engaging DOR records automatically through the handoff holds. Retain both matching CSV files for review. REC alone never engages flight control.

Methods

• Aerobraking uses atmospheric drag to remove orbital energy. It is not a promise that a Rise vehicle can tolerate an arbitrary unpowered entry. NASA's Mars Reconnaissance Orbiter first used a propulsive maneuver to enter Mars orbit, then spent about five months aerobraking to reduce that orbit. It did not take six months to first achieve orbital velocity. NASA mission operations reference.
• Powered entry combines engine braking with aerodynamic lift and drag. Rise ships use Iagreous fuel, but available thrust, loaded mass, engine response and atmospheric limits still matter. Reducing speed before entering denser air gives more margin than waiting for a warning and then demanding maximum reverse thrust.
• TVM is a velocity-control aid, not a complete entry controller. Its setting uses the selected target/reference and the ship's forward axis; it is not an airspeed or temperature limit. With a surface waypoint selected it uses a ground reference. See TVM and verify the selected target before engagement. TVM can command sustained thrust while opposing gravity, lift or drag; it does not guarantee suitable attitude, terrain clearance or a safe arrival.

Normal re-entry attitude

The manual example assumes wings level, with the nose generally into the relative airflow and the flight path aimed toward the destination. Pitch attitude and flight-path angle are different: monitor both instead of assuming the ship travels exactly where its nose points. Reverse main thrust permits braking while retaining a forward-facing attitude; lateral and vertical RCS have separate limits.

Deciding When To Drop

A heavy ship takes more time and distance to decelerate at the same thrust. Worked example, not a universal procedure: the original technique below assumed about 1.2 G acceleration in vacuum. Its distances, speeds and pitch angles depend on the vehicle, load and starting trajectory; do not use them as certified limits.
Vieneo has no sharp atmospheric boundary. Its modeled density falls with a 7.5 km scale height; pressure, temperature and air-relative speed matter at the actual altitude. Its nitrogen-rich atmosphere is denser at the surface than Earth's, so Earth entry schedules are not interchangeable. At high altitude lift and drag may be weak, but 100 km is not a guarantee of negligible heating or dynamic pressure.
The worked example began reverse thrust at 100-120 km MSL, roughly 1500-1300 km from the target, and used upward translation to limit descent until ground speed was about 3 km/s. Those are example conditions, not a rule for when to start braking. A different mass, plane or arrival deadline can require substantially more distance.
In that example the ship then descended at roughly 2.5-3 km/s with the nose about 15 degrees below the horizon, while reverse thrust continued. Translation helped keep the flight path near the nose direction until aerodynamic lift could provide more control. Do not hold a fixed pitch regardless of IAS, AFT, dynamic pressure or descent trend. Use the configured upward/downward translation controls as required; the direction of the vehicle response matters more than a default key label.

Both air-relative speed and descent rate matter. Dynamic pressure varies with mass density and the square of air-relative speed. Heating also depends strongly on speed. Descent rate determines how quickly you encounter denser air; it does not make forward speed harmless.
Do not treat 5 km/s at 100 km, or any other speed/altitude pair, as universally safe. Watch AFT, IAS/Vne, dynamic pressure, flight path and available braking margin before conditions reach their warnings.

Slowing Down

The example aims to reach roughly 30 km MSL and 0.5 km/s before ordinary atmospheric flight. A 15-degree pitch does not guarantee that result. The planner uses 30 km / 0.5 km/s TAS as an adjustable test handoff, with the remaining glide reach estimated upstream of the destination. The pilot must still manage atmospheric descent, ATC routing, terrain and the final approach. Higher or faster handoff settings are test choices, not automatically validated alternatives.

Points to Remember

• Avoid abrupt pitch or translation commands against large aerodynamic loads. To reduce descent, command the appropriate upward vehicle acceleration and adjust pitch within the available lift and load margin; do not confuse downward exhaust with downward vehicle motion.
• Do NOT roll inverted!
• If you are going to overshoot, prioritize a controllable trajectory over reaching the waypoint. Level off only if lift, thrust, airspeed and terrain permit it, then plan another approach.
• Do not force a late turn or steep descent to reach the target. Use practice flights and recorded results to establish repeatable margins for your vehicle and load.
• Your instruments are your friends, they will show you when danger is approaching, not the window.
• STAY CALM AND DO NOT PANIC!

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