The History Of Space Flight Computer Science Essay

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: It has been well said from NASAs DEEP SPACE - REMOTE site that, its one small step in the history of space flight. But it was one giant leap for computer-kind, with a state of the art artificial intelligence system being given primary command of a spacecraft.

Artificial Intelligence is such a field of study that seeks to explain and emulate intelligent behaviour in terms of computational processes that it is now widely being used in NASA in its space explorations missions and experiments. One such software, about which I am going to discuss here, is CASPER (Continuous Activity Scheduling Planning Execution and Replanning) which has been designed to perform automated planning of interdependent activities within a system for particular requirements, constraints, and limitation o resources.


What is Artificial Intelligence?

Artificial Intelligence is simply the science and engineering of making intelligent machines that can perform those tasks which any human being can do by applying intelligence.


Earlier, when the satellites were sent to the space, they were engaged or stuck in a laborious tasks like locomotion, took longer time than expected in communications with ground controllers.

Whatever the data was collected was sent back to earth in form of beams, which was either in good condition or bad and then after taking decisions humans sent the command to operate. It was all a very risky and tedious job as risk of loss of data is involved.

How would it be if a machine or a satellite in space can take decisions on its own and only send informative data back to earth, not everything like regarding movements, directions etc. ?

It has been made possible that machines can take decisions on their own even when they are in space or any other place. For this, machines should need software which governs it, what decisions to take. One such software named CASPER (Continuous Activity Scheduling Planning Execution and Replanning), is being used by NASA in its space exploration missions.


Traditionally, all the spacecrafts which were sent in the space exploration missions; were controlled by the mission control centre on earth i.e. spacecraft did what mission control (at earth) ordered it through commands. It acted like a puppet i.e what was ordered to it, it does.

The Artificial Intelligence group at the Jet Propulsion Laboratory (JPL) in Pasadena, USA, made the software named CASPER through which spacecraft being sent in the space will be able to make decisions on their own.

All the moves, in which direction to move the spacecraft and all similar decisions will be taken by the software itself. This will reduce the signal transmission for each and every move (either small or big) up to large extent. In other words we can say that, earlier if any command that comes from the ground or response signal is sent back to earth, it takes long hours. But NASA's Continuous Activity Scheduling, Planning Execution and Replanning (CASPER) software will respond instantly as it itself is the decision maker.

Studies have shown by using data from NASA's Galileo spacecraft that the software would have reduced the signals transmission time by 100 to 200 times as compared to the time it took earlier.

Before the invention of project CASPER, planning process was used in the space exploration machines which followed batch-oriented model but this model proved to be inappropriate for the space going vehicles because this model fails to be responsive and making decisions anytime.

Traditional Batch-oriented model

To overcome this drawback, the scientists at the Jet Propulsion

This is a snapshot of working ASPEN software.

Laboratory (JPL) developed CASPER system which was the real time and effective version of the previous project known as ASPEN (Automated Scheduling and Planning Environment).

Now, instead of batch oriented process which considers two aspects: 1) initial state

2) Goal state, CASPER possesses:

  • Current status
  • Current goal state
  • Future predictions
  • Current plan


There are huge benefits of using Artificial Intelligence technology in space exploration missions as with this technology machines can make most of the decisions on their own. When the spacecraft is bind with the Artificially Intelligent software (which at present is CASPER) then it possesses numerous benefits. Some of the important of them have been listed below:

  • The spacecraft will become more responsive to unexpected changes in the surroundings. If it needs to move to some other place instantly may be due to any change in the climatic conditions etc, then it will decide on its own and will move to the safer place rather than sending signal to earth about its current location and wait for the signal to return which guides it to move to some other safe place.
  • According to the scientists in Jet Propulsion laboratory (JPL), the software CASPER will update its plans continuously according to the environment in which it will be and can reduce its dependency on the predictive models like inevitable modelling errors.
  • As replanning is done after scheduling, planning and execution step so Fault protection and execution layers will take a very less span of time in controlling the spacecraft.
  • This will save a lot of time which otherwise would go wasted in transmitting unimportant data
  • Lot of power, however, is saved by taking real-time decisions.


CASPER is an onboard Artificially Intelligent software that performs the decision-making function for the spacecraft. In simple terms I can say that as we see things around us through our eyes, hear from our ears and manipulate things and take decisions with the help of our brain; in similar fashion CASPER works i.e. it takes data from the spacecraft sensors such as cameras, and many other type of sensors and make decisions based on that data to carry out the mission. It uses continuous decision making to support modification and updating of a current working plan without any interruption.

CASPER actually works in three phases:

  • in first phase, planning and scheduling is done
  • in second phase, planning and execution is done
  • in third phase, replanning is done

Actually, this software has a current goal set, a plan, a current state, and a model of the expected future state. After achieving its goal state or a path to reach a goal state, it continuously updates the new state as its current state and aging invokes the planning and replanning process.

Wherever CASPER is used, it follows a Local Search Algorithm or Framework or iterative repair algorithm to solve planning and scheduling problems at a faster pace.

The above snapshot is of the simulator which works as CASPER showing its various components and its working.

CASPER follows Continuous Planning Incremental Process which is shown as follows:

Continuous Planning Incremental Plan Extension followed by CASPER

Change of planning process merely takes 1 to 10 seconds of time which means it remains highly updated then the previous technologies. Therefore, it is also known as short term planner. The various characteristics of this short term planner are listed below:

  • It makes a queue of observation and decides intelligently which observation to consider next.
  • It considers all the targets which are present on its list, their visibility windows and their relative positions in the space.
  • It also tracks other resource management issues like data management, relative science and engineering observations.


CASPER focuses on Generic (means General) Planning and Scheduling application framework that can work on CASPER's various components are as follows:

  • An expressive modelling language to allow the user to naturally define the application domain.
  • A constraint management system for representing and maintaining domain operability and resource constraints, as well as activity requirements.
  • A set of search strategies and repair heuristics
  • A temporal reasoning system for expressing for expressing and maintaining temporal constraints.
  • A graphical interface for visualizing plans and schedules.
  • A real time system which monitors plan execution and modifies the current plan based on activity, state and resource updates.


CASPER has created a revolution in the space exploration missions. After its invention in the year 2002, it has been widely under use and is embedded in all the space exploration missions. It has been largely used in automation applications such as listed below:

  • Spacecraft
  • Rovers
  • Ground Communication Stations
  • Non piloted planes and jets (example can be taken from the movie STEALTH)

Moreover, invention of CASPER lead to operation of Space Infra-red Telescope Facility (SIRTF) because much faster response time of CASPER. This telescope aims at targeting Earth special spots.

CASPER has also been used in the three Corner Sat (3CS) University Nanosat mission of space. CASPER helped the 3CS mission in tougher tasks such as: data validation, replanning, robust execution, multiple model-based anomaly detection, control and formation flying. This usage of CASPER is known as Autonomous Spacecraft Constellation (ASC).

CASPER also finds its usage in the fields of number of research prototypes in various applications such as: autonomous rovers, deep space communication station communication.