Constellations of satellites for a space-based internet are coming.

Screen Shot 2018-11-18 at 4.41.31 PMHere is the space debris and satellites NOW circling Earth.  It’s about to get even more crowded with 8,000 MORE  satellites. Their use as K-band type Internet satellites means THE WORLD WIDE WEB becomes quite literal.

SpaceNews

 

POINT

These internet satellites will be placed in low-Earth orbit (LEO) and very low Earth orbit (VLEO).  SpaceX will launch the majority of such satellites into VLEO orbits beginning at <200 miles above the Earth.

Operating in these orbits can provide a number of benefits to Earth observation and communication spacecraft as the spacecraft operates closer to the observer.  These benefits allow the performance of platforms in higher orbits be matched with simpler and smaller platforms in VLEO.  This can result in smaller spacecraft and hence in lower costs.  Anything placed in lower Earth orbit is cheaper than boosting it to higher, geo-synchronous orbit.

Flying at such low altitudes also means flying through a denser part of the atmosphere and thus increased aerodynamic forces. These higher aerodynamic forces can be seen as challenge, but they can also represent an opportunity. These forces can be used for orbit and attitude control, and to de-orbit spacecraft well below the 25-year Inter-Agency Space Debris Coordination Committee (IADC) guideline.  Potential shorter orbital lifetimes (due to increased drag) can also represent an opportunity for constellations to replenish their fleets of smaller spacecraft more frequently and thus become more responsive to technology and market changes. In this paper, the different benefits of VLEO with respect to traditional high altitude orbits are quantified considering both optical and Synthetic Aperture Radar (SAR) payloads.

The challenges and opportunities emerging from the significant increase in aerodynamic forces are discussed, with some examples of aerodynamic orbit and attitude control provided. The debris resilient properties of these orbits are briefly quantified and discussed with different lifetimes scenarios analyzed (from different combinations of altitudes and ballistic coefficients). Finally, several concept studies that highlight the main design drivers of platforms operating at such orbits are briefly presented.

COUNTER-POINT

However, 1-in-5, or 20% of all Cubesats in LEO and VLEO exceed the 25-year IADC guideline.*  Regarding  guidelines for the disposal of cubesats, almost no codes of conduct, guidelines, regulations or laws are stated in a manner that is measurable, verifiable, or enforceable.

The frequently misunderstood guideline that post-mission orbit lifetime be no longer than 25 years is inapplicable until it is too late to act.  If it is violated, there is no action that would change the threatening environment.

In a letter to SpaceNews in 2015

“No law or regulation can reasonably require any specific lifetime. The operation of a satellite would have to be monitored continuously throughout its life, and the near-Earth space environment would have to be characterized regularly to assure satellite disposal. International Organization for Standardization (ISO) 24113, Space Debris Mitigation, which attempts to make IADC guidelines normative, violates the fundamental principles and rules of standardization, that requirements be measurable and verifiable.

Authorities and customers must confine requirements to what can be acted on and observed in time to invoke actions that could mitigate consequences. We can require only verifiable and correct analyses and tests that support estimates of lifetime, potential fragmentation, and collision avoidance throughout a satellite’s life.

These should employ reasonable and rational projections of the space environment. All of this is uncertain. The uncertainty increases with time in orbit. No authority or expert can guarantee that lifetime will be 25 years. Given the same starting data, diverse and equally credible orbit lifetime estimates vary by years.

Requiring all to adopt any institutionally unique or proprietary technique is restraint of trade. All stakeholders might not be capable of doing it that way. The U.S. Federal Communications Commission requires an end-of-life disposal plan that demonstrates intent and ability to remove a satellite within 25 years. It does not require a 25-year lifetime. The only verifiable element of ISO 24113 is a debris mitigation plan. A 25-year post-mission lifetime cannot absolutely be required a priori.

Each agency or authority should judge the veracity of analyses presented to gain launch and operational licenses. They might individually accept different levels of risk. If they were overly optimistic and there were incidents, they must bear the consequences. But all would be at risk, and none has the prerogative to decide what risk is acceptable to others.

We must not forget that the goal is to minimize debris and avoid collisions, no matter how long a satellite might remain in orbit. The 25-year guideline is poorly cast and unenforceable.”

Dave Finkleman
Colorado Springs, Colorado USA


 

* “One of every five Cubesats launched between 2003 and 2014 does not meet international guidelines calling for satellites to deorbit – by force of nature or their on-board systems – within 25 years of retirement,” NASA said.

“Depending on how the data is read, the United States is both the biggest single offender and a better-than-average participant in the cubesat business when measured by orbital debris-mitigation practices,” NASA said.

In the July 2015 issue of Orbital Debris Quarterly News, produced by the NASA Orbital Debris Program Office at the Johnson Space Center in Houston, the agency provides fodder to both sides of the debate over whether the increasingly popular cubesats are a threat to orbital-highway safety.

Cubesat is a term measuring a satellite’s approximate size and mass. A 1-unit cubesat is a 10-centimeter cube weighing about 1 kilogram. Most launched so far are in the 1- to 3-unit size, but the industry is expanding so rapidly that these early trends may not endure.

Most cubesats have no on-board propulsion. Many cubesat owners are obliged to take such launch opportunities as are available to them, even though their spacecraft, as secondary payloads, must accept whatever orbit is required for the rocket’s main customer.

This is why cubesat owners are often unable to tell regulators, or other satellite owners, exactly what their operating orbit will be when they announce their programs.

Having to hitch a ride to orbit however they can get it, cubesat owners have said they sometimes face a Hobson’s choice of scrapping their entire mission or accepting a launch to an orbit in which their spacecraft will remain for many decades after operational lives of two years or so.

Orbital debris experts calculate how long a satellite will remain in orbit by its orbital parameters and by the satellite’s area-to-mass ratio, which provides indications of how quickly its orbit will decay naturally from the drag of the residual atmosphere in low Earth orbit.

Using data from the U.S. Air Force’s Joint Space Operations Center at Vandenberg Air Force Base, California, NASA counts 231 cubesats launched between 2003 and the end of 2014, not including 44 lost in launch failures.

61% of these satellites are U.S.-owned Twelve of these U.S. spacecraft are in orbits from which they will not reenter the atmosphere within 25 years and are thus do not meet international guidelines.

Another 26 have satellite and orbital characteristics that make it impossible to determine how long they will remain in orbit.

While their numbers are much smaller, non-U.S. cubesats have performed worse than their U.S. counterparts when measured by atmospheric reentry dates: More than one-third of the 90 non-U.S. cubesats will remain in orbit more than 25 years after they stop functioning, NASA says.

Cubesats operating in orbits with perigees below 600 kilometers in altitude will usually meet the 25-year rule. Orbits between 600 and 700 kilometers “are on the boundary” and may or may not meet the guideline, NASA says. The International Space Station, which is serving as a platform for cubesat launches, flies at around 400 kilometers in altitude, meaning satellites launched from there will almost invariably deorbit within 25 years.

Above 700 kilometers, “all cubesats display longer in-orbit lifetimes and non-compliant residence times,” according to NASA.

There is no known case of a cubesat, dead or alive, colliding with another object in low Earth orbit. But the effervescence of the cubesat industry — and more generally, the current production rate of small satellites — is such that the situation in low Earth orbit is likely to be much different in five years.

Recognizing the problem — and wanting to avoid being freighted with even well-meaning regulatory burdens if debris concerns become more pressing — some cubesat owners are designing debris-mitigation into their satellites.

Adding on-board propulsion is currently out of the question for many cubesat programs given the additional manufacturing and launch-cost increases this would entail. But they can add lightweight hardware to their satellites that would deploy on retirement, increasing the area-to-mass ratio and acting as an orbital brake, forcing the satellite down to where it reenters the atmosphere more quickly. – SpaceNews, 2015


 

Leave a Reply

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s