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History of the HL-20


In Aeronautics industries, the simulation does the key role, because of the complexity. When we do the testing by prototype it takes considerable time, quite expensive, and difficult to check the results while change the parameters.

The spacecraft landing has an account with considerable practical and analytical problem because of the unpredictable external-environmental parameters i.e. weather, wind.

The HL 20 is the NASA designed model for a manned spaceplane, known as Crew Emergency Return Vehicle (CERV) or Personal Launching System (PLS). The concept of the PLS has been developed to carry six to eight men to space stations. 


Total length - 8.9 m (29 feet)

Maximum Diameter-wingtips - 7.2m (23.5 feet)

Total habitable volume - 16.3 m3

Total mass - 10 884 kg

Total payload - 545 kg

A lifting body is basically a wingless vehicle that flies due to the lift generated by the shape of its fuselage. researchers  including Alfred Eggers at the NASA Ames Research Center conducted early wind tunnel experiments find that half of a rounded nose -cone shape that was flat on top and rounded on bottom could generate Lift Drag ratio of about 1.5 to 1.

Literature Survey

History of the HL-20

After the 2nd world war the powerful countries were competing to dominate the revolution of the space world, yield in 1969 the America attained their first step at moon. After revolution in space world, the requirements to use the spacecrafts are rapidly increased in last decades.

In 1983, Vehicle Analysis Branch began the investigation of BOR small space plane being orbited several times by the Soviets starting in 1982 and recovered at in the Indian Ocean and Black sea. During the recovery operations of the space plane in the Indian ocean, an Australian P-3 Orion aircraft obtained photographs of the vehicle both floating in the water and being hauled aboard the recovery ship.  [2]. this provided the valuable insights into the shape, weight, and center of gravity of the vehicle. Based on this information, small wind tunnel models were manufactured and tested by NASA.the results demonstrated that, the vehicle had got good Aerodynamic characteristics throughout speed range from orbital entry interface to low supersonic speeds. Wind tunnel tests configuration directional stability at all speed from Mach 20, trimmed to maximum L/D with 10 degree elevon deflections in subsonic range.

Lifting Body Heritage

Lifting body concepts were proposed for transporting people to and from space in late 1950s. In those days NASA Langley Research Center developed a lifting body known as HL 10 it could carry 12 people and be launched on a Saturn IB booster with about 15000lb of payload to service an orbiting space station. But the HL-20 design approach was received Dec 10 1992  rivision received Feb 15 1983accepted for the publication Feb 17 1993. [1]. The NASA Ames Research center developed the M2-F2 lifting body concept, for this mission whereas the US AirForce developed the X-24 lifting body concept for military purposes.each of these configurations was propelled the extensive research and wind tunnel testing.

Very beginning of the research periods, the primary goals included the definition of concepts that would be reusable and have minimal operational refurbishment requirements, low entry accelerations, fixed geometries, runway landing capability, and a minimum of a once-per-day return capability to the USA. The specific vehicles goals were the achievement of a Lift Drag ratio grater than 1 at hypersonic speeds, high trim-lift coefficient, Lift Drag ratio grater than 4 at subsonic speeds, high volumetric efficiency, static stability and controllability of all speeds and of course compatibility with projected launch vehicle. [1].

HL 10 Lifting Body

The vehicle length was 21.17 feet. The launch weight with propellants was 10 009 lb and the landing weight was 6473 lb, the center of gravity range from 53.14 percent of the body length for the launch weight configuration to 51.82 percent for the landing condition.

From: NASA Reference publication 1332 1994 HL-20 chronologies

History of simulation

In last decades of the twentieth century, AIAA Modeling and Simulation Technical Committee were involving to develop the aircraft/spacecraft models. When they developed the simulations they had identified and include the basic simulation parameters for airframe model such as function tables, block diagram, mathematical equation (nonlinear partial equations) and verification test data to check the data before shear the data with another modal. The data should be able to interpret to the standard format or code by the internal architect of the simulation.

In late 1990s they developed candidate format to the aerodynamic section of the simulation model i.e. if want to clear or exchange the data, mathematical equations, definitions and the function tables are required.

When we consider the HL-20 NASA model the aerodynamic model contains 51 variables such as 168 one - and two dimensional table, four breakpoint sets, and total of 6240 data point. It defines the outputs for six aero dynamic coefficients i.e. Cx, Cy, Cz, Cl, Cm, Cn as a function in angles of attack (AOA) angle of slide ship, Mach number, Airspeed and angular body rate. This includes the non linear function as interpolated tables, switches and absolute value elements in the variable definitions.

From Evaluation of a Candidate Flight Dynamics Model

Simulation Standard Exchange Format

E. Bruce Jackson* NASA Langley Research Center, Hampton, VA 23681

Bruce L. Hildreth† SAIC, Lexington Park, MD 20653

Brent W. York‡ Naval Air Systems Command, Patuxent River MD 20670 and

William B. Cleveland§ Northrop Grumman Information Technology, Moffett Field, CA 94035

Chapter 2

Theoretical analysis

Modelling assumptions and limitations

The simulation of the spacecraft system is complicated system, so for easy work and analysis we assume the model or geometry of HL 20 as follows.

The Mach number is an important parameter in flight mechanics; it can be calculated by the following equation

According above equation the Mach number is depended on fluid velocity. If the fluid can be compressible, the surrounded fluid of the airspeed indicator velocity can't be the same as outside fluid velocity. And also the compressibility can vary with respect to the speed of the airframe. Therefore we assume the fluid is incompressible.