# Low-Density Supersonic Decelerator

> NASA vehicle which tested an inflatable reentry system

**Wikidata**: [Q17297602](https://www.wikidata.org/wiki/Q17297602)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Low-Density_Supersonic_Decelerator)  
**Source**: https://4ort.xyz/entity/low-density-supersonic-decelerator

## Summary
The Low-Density Supersonic Decelerator (LDSD) is a NASA technology-demonstration spacecraft that flight-tested inflatable atmospheric-entry systems for future Mars missions. It combined a rocket-powered test vehicle with two large, pressurized decelerators designed to slow payloads traveling faster than the speed of sound in the thin upper atmosphere.

## Key Facts
- **First rocket-powered test flight**: 28 June 2014, 18:45 UTC  
- **Second rocket-powered test flight**: 8 June 2015, 17:45 UTC  
- **Funder / operator**: National Aeronautics and Space Administration (NASA)  
- **Instance of**: reentry vehicle and technology demonstration spacecraft  
- **Aliases**: LDSD, Desacelerador supersónico de baja densidad  
- **Official project page**: https://www.nasa.gov/ldsd/ (English)  
- **Commons category**: Low-Density Supersonic Decelerator  
- **Freebase ID**: /m/0113xfpx  
- **Wikipedia sitelinks**: 10 language editions (ar, de, en, es, fa, fr, it, pt, uk, commons)  

## FAQs
### Q: What did the LDSD project actually test?
A: It tested two inflatable decelerators—a Supersonic Inflatable Aerodynamic Decelerator (SIAD) and a large supersonic parachute—by lofting them to high altitude with a rocket sled and then deploying them while traveling faster than Mach 3.

### Q: Why were the tests conducted over the Pacific Ocean?
A: The ocean provided a safe, uninhabited area to recover the test vehicle after it splashed down, and a high-altitude balloon could lift the rocket sled to the required 120,000 ft starting point.

### Q: Are the LDSD technologies intended for Earth re-entry or Mars landing?
A: They are sized and optimized for future robotic and human-scale Mars landers that need to decelerate heavy payloads in the planet’s thin atmosphere.

## Why It Matters
Current Mars entry, descent, and landing systems are limited to about 1.5 metric tons of landed mass—far below the 20-plus tonnes a human mission would require. LDSD’s inflatable heat-shield and parachute technologies could increase the usable entry mass by a factor of two to three, opening the door to larger rovers, sample-return landers, and eventually crewed spacecraft. By demonstrating stable inflation and controlled deceleration at supersonic speeds, LDSD reduced the risk of incorporating these lightweight, stowable decelerators into future planetary missions, potentially saving hundreds of kilograms in traditional rigid heat-shield mass and launch volume.

## Notable For
- First successful deployment of a 6-meter-class inflatable decelerator at Mach 3+  
- Demonstrated real-time telemetry of inflation pressures and aerodynamic stability during supersonic flight  
- Used a high-altitude balloon plus rocket sled to reach Earth-relevant dynamic pressures similar to Mars entry  
- Served as pathfinder for next-generation Mars landing systems without requiring an interplanetary mission  

## Body
### Development and Objectives  
NASA’s LDSD project began under the Space Technology Mission Directorate to mature “game-changing” entry technologies for high-mass Mars payloads. The two primary hardware elements were the Supersonic Inflatable Aerodynamic Decelerator (SIAD), a pressurized ring that increased the vehicle’s diameter from roughly 4.7 m to 6 m, and an 30.5-meter disk-gap-band parachute. Both had to survive dynamic pressures above 1 kPa while traveling faster than 450 m s⁻¹.

### Flight Campaign  
A helium balloon lifted the 3,175-kg test vehicle to ~37 km. A Star-48 solid rocket then accelerated the stack upward to ~55 km, where the SIAD inflated within 0.5 s. After several seconds of stable deceleration, the parachute deployed and slowed the vehicle for ocean splashdown. The 2014 flight achieved full SIAD inflation; the 2015 repeat focused on parachute performance. All data were telemetered in real time to recovery ships and airborne relays.

### Outcomes and Legacy  
Both flights validated computational fluid-dynamics models for inflatable structures at supersonic speeds and provided high-resolution pressure, temperature, and acceleration datasets. Although the 2015 parachute experienced partial failure, the overall program met its metric of advancing TRL (Technology Readiness Level) from 4 to 6, qualifying the SIAD for potential infusion into future Mars missions.

## References

1. [Source](https://www.americaspace.com/2014/07/01/nasas-low-density-supersonic-decelerator-test-flight-hailed-as-a-success/)
2. [Source](https://www.nasa.gov/press-release/nasas-ldsd-project-completes-second-experimental-test-flight)
3. [Source](https://www.nasa.gov/pdf/737628main_Final_LDSD_Fact_Sheet_3-26-13.pdf)