Thursday, April 22, 2010

SBAS Crashing

April 21, 2010 By: Eric Gakstatter

Survey Scene, April 2010


It’s been a tough couple of weeks for SBAS (Satellite-Based Augmentation System), namely the USA’s WAAS program and India’s GAGAN program. WAAS and GAGAN have taken big hits recently that threaten the integrity of the programs. Both events were totally unexpected and are causing disruptions of GPS correction services.

Let’s Start with WAAS

First of all, consider the following infrastructure graphic describing WAAS.



WAAS Infrastructure (note: GEO satellites positioning not geographically correct in graphic)

At the moment, WAAS uses two geostationary satellites (referred to as GEOs) to broadcast GPS corrections throughout the WAAS service area, which covers the U.S., Mexico, and most of Canada. The user’s GPS receiver must be able to “see” at least one of the WAAS GEOs in order to receive the GPS corrections. Currently, one WAAS GEO (PRN 135) is located at 133°W longitude and one (PRN 138) is located at 107°W longitude. They are positioned, for the most part, to provide “dual coverage” in case one fails as the following graphic illustrates. The solid line represents the visibility above the horizon of PRN 138 (107°W). The dashed line represents the visibility above the horizon of PRN 135 (133°W). In New York, for example, PRN 138 is visible at 30°+ above the horizon while PRN 135 is visible at ~15° above the horizon.


WAAS GEO Footprint Coverage (Dashed = PRN 135, Solid = PRN 138)

The Federal Aviation Administration (FAA) is the WAAS steward. WAAS (and SBAS) was designed for aviation use and paid for by the FAA. The fact that surveying and mapping users benefit from WAAS is a by-product. The FAA owns and controls most of the WAAS infrastructure, such as the 38 WAAS reference stations located throughout the U.S., Canada, and Mexico. About the only thing they don’t own are the WAAS GEO satellites, and this has been the source of most of the problems with WAAS in the past few years.


Lease vs. Buy

It would be prohibitively expensive for the FAA to own GEO satellites that were exclusively used by WAAS. Instead, the agency leases bandwidth from owners of commercial satellites. These are the same commercial satellite owners who lease bandwidth to media (e.g., television) customers. It’s not unlike a utility pole you see along the road with many different wires and devices attached to the pole from different companies who pay to lease space on the pole, except it’s a very expensive pole orbiting in space.
If you’ve been using WAAS for a number of years, you’ll remember back in 2006 there was a hiccup with the WAAS GEOs at that time. The FAA was leasing space on two Inmarsat satellites (AOR-W and POR). They began transitioning to the current WAAS GEOs but before the transition was complete, Inmarsat began moving AOR-W. This was a headache for some WAAS users and really showed the vulnerability of WAAS.


Losing Control

The vulnerability reared its ugly head again last week when one of the commercial satellite operators (Intelsat) that the FAA leases space from announced it had lost contact with its Galaxy 15 (G-15) satellite, which is the GEO that WAAS PRN 135 is broadcast from. Intelsat reported it had lost the ability to send commands to G-15. Without the ability to control the satellite, it will slowly drift out of orbit until it becomes unusable. The FAA estimates this will occur in one to three weeks.


Solutions?

Intelsat’s answer was to bring in an older generation backup satellite (G-12), which was in a backup orbit at 122°W. It arrived at 133°W around April 14. Intelsat said that G-12 has virtually an identical C-band package as the G-15 and they could transfer C-band customers to the G-12. The problem is that there is no L-band package (which WAAS needs) on the G-12, so the FAA was out of luck.


Since Intelsat’s G-12 backup won’t help WAAS, the FAA is looking at other alternatives:

  1. Contract with Inmarsat to bring back POR (178°E). The FAA says that will take 12-18 months. Personally, I don’t think it’s a good solution. It’s too far to the east to help much at all. Its coverage footprint barely covers the western U.S.
  2. Speed up the testing on the new PRN 133 (98°W) and bring it into service more quickly than the original December 2010 schedule. The FAA says it can accelerate testing by one to two months. This is good and I see the benefit, but it still doesn’t help Alaskan users.
  3. The replacement backup satellite being moved to 122°W to backup G-12 may be a solution. It will be a few weeks before it is known what is possible. That would be the best scenario from a coverage footprint standpoint. The question is how long it would take to bring it into service.
On another note, the FAA stated that with the money they are saving with G-15 going out of service, they will be able to accelerate the acquisition of another WAAS GEO. I have no doubt that this has put a new level of fear into the FAA folks, and they have to realize that they can’t be running thin on WAAS GEOs. If you weren’t aware, the future of aviation navigation is based on GPS, WAAS, LAAS, etc. These sorts of hiccups would be an absolute nightmare if the National Airspace System (NAS) was already dependent on GPS.


GAGAN

GAGAN (GPS-Aided Geo Augmentation Navigation) is India’s SBAS. It has been under development for many years and is quite far along in development. It is funded through implementation by the Airport Authority of India with the Indian Space Research Organization. In 2008, GAGAN was broadcasting a test signal from an Inmarsat GEO with reasonable results.

India’s intent was to launch its new GSAT-4 communication satellite with part of its purpose being a GAGAN GEO satellite. GSAT-4 was to be India’s first rocket with an Indian-designed and built cryogenic-fueled third stage. Apparently it is a very difficult technology to master as it reportedly took India 16 years to develop.

Last week, after much anticipation, the rocket with GSAT-4 onboard was brought to the launch pad. Liftoff was reportedly flawless. At 8:25 minutes into flight, the rocket failed and the entire rocket, GSAT-4 and all, ended up splashing into the Bay of Bengal. It’s a crushing blow to India’s GAGAN SBAS program, which has suffered a number of delays.

P.S. Veeraraghavan, director of the Vikram Sarabhai Space Centre in Thiruvananthapuram, said “Our target is to fly a GSLV with our indigenous cryogenic engine within one year. But it will be tough.”

Thursday, January 14, 2010

New 24+3 GPS Configuration Will Increase Accuracy


Moving three existing GPS satellites to new orbit locations will have a profound effect on GPS capabilities for all civil, commercial, and military users worldwide.


The U.S. Air Force Global Positioning Systems Wing and the 50th Space Wing have announced a reconfiguration: the 24+3 GPS constellation plan or “Expandable 24,” with timeline as follows:

“The [24+3] initiative will take up to 24 months to fully implement as satellites are repositioned within the constellation based on constellation health. The beneficial impact to all GPS users, including civilian users, will be slowly realized during that time period. Over the next two years, the number of GPS satellites in view from any point on earth will increase, potentially increasing accuracy of GPS receivers.”

The plan will significantly alter the current configuration, which consists of indeed 30 GPS satellites in MEO or medium earth orbit that are used globally, however many of the additional satellites are currently flown in tandem, side by side, with considerably older satellites and effectively limit the constellation geometry to that of 24 satellites.

Further details will come in this week’s Defense PNT newsletter, in a column by GPS World contributing editor Don Jewell.

Meanwhile, the Wing and GPS 50th Space Wing also announced that they “are ushering in improved Global Positioning System (GPS) capabilities through a new ground system software release. New capabilities include telemetry, tracking and commanding for the new GPS IIF space vehicle and robust security improvements. The planned transition at Schriever Air Force Base on January, 11, 2010, is the result of extensive testing to ensure this upgrade is transparent and has no impact to military and civil users."

The Space Wing continued, "With the pending mid-2010 launch of the first GPS IIF space vehicle, the ground system is prepared to command the new on-orbit GPS IIF capabilities which include a new navigation signal for civil users, encrypted military code, crosslink enhancements, improved navigation signal accuracy and signal power increases. The new software also provides robust security improvements to include 'over-the-air' distribution of encryption keys to properly equipped military users. Preparation for activation of the new software included rigorous developmental and operational testing events including five transition exercises. The new ground system software commanded current individual GPS satellites during numerous testing events and rehearsals. In November and December 2009, the new software successfully uploaded operational GPS IIA and IIR space vehicles with navigation data and completed normal operational functions. This improvement initiative continues the Air Force’s commitment to the global community of GPS users."

The GPS Wing statement continued, "The U.S Air Force and Air Force Space Command have been the diligent stewards of GPS since its conception in the 1970s and continue its commitment to this critical component of our National Infrastructure. The current GPS constellation has the most satellites and the greatest capability ever. We are committed to maintaining our current level of service, as well as striving to improve service and capability through on-going modernization efforts. The Air Force will continue to pursue an achievable path maintaining GPS as the premier provider of positioning, navigation and timing for military and civilian users around the world."

The Air Force Space Command’s Space and Missile Systems Center, located at Los Angeles Air Force Base, Calif., is the U.S. Air Force’s center of acquisition excellence for acquiring and developing military space systems including six wings and three groups responsible for GPS, military satellite communications, defense meteorological satellites, space launch and range systems, satellite control network, space based infrared systems, intercontinental ballistic missile systems and space situational awareness capabilities.

source: GPS World

Sunday, January 10, 2010

Opinion: GPS L2P(Y) Phase Shift Causes Needless Consternation January 6, 2010 By: Don Jewell

Roughly three years ago, the U.S. military conducted the first flex-power test on the L2 GPS codeless signal. Almost immediately, the civilian GPS community expressed concern that future changes to the L2P(Y) signal power levels might cause a signal phase shift; such a phase shift would be incompatible with equipment using the P(Y) signals in a codeless/semicodeless fashion for extremely accurate positioning applications.

Civilian users were naturally upset because they had invested millions of dollars in systems that might not be usable — even if the unusable periods were of a very short duration.

The National Positioning, Navigation, and Timing (PNT) Executive Committee responded by tasking the National PNT Engineering Forum (NPEF) to look at the problem. Within a few months, the NPEF announced a solution: flex power could be used in such a manner that it would not cause a phase shift. At the same time, the military reminded civilian users that the codeless use of L2P(Y), as accurate as it might be, was never intended and should not be a long-term solution.

An agreement was reached between the U.S. government and civilian users that the civilian users of this codeless/semicodeless technique would migrate from using the L2P(Y) carrier to using the new L2C signal to achieve not only the same, but better results. To codify this agreement, a Federal Register Notice was issued in 2008 identifying the terms of this agreement, which guaranteed the phase stability of the current L2P(Y) signal until 2020. This gives civilian users 12 years to figure out a migration plan and to obtain adequate use of the equipment they already have on hand.

In addition, 2020 is not a drop-dead date, but a date when the use of L2P(Y) codeless signals will no longer be guaranteed, though may well still work. Who knows what PNT advancements will take place between now and then? This could very well be a moot point by then, and in my opinion should be one now.

Problem Solved? Apparently not. A lag between the issuance of this national policy and analogous adjustments to interface specifications caused consternation within the civilian community. Misunderstandings added to this perceived impasse. Various solutions were identified to work around this looming quandary. However, given the national policy to support codeless/semicodeless use until 2020, the Air Force Space Command commitment to that policy, and the recommendations of the NPEF, these solutions seem wholly unnecessary to me.

The U.S. government has gone well beyond what is required to ensure civilian codeless and semi-codeless users are accommodated.

For the foreseeable future, users will be able to employ L2P(Y) codeless/semicodeless techniques for very accurate position determination and will not have to worry about phase shifts disrupting their work.

— Don Jewell, GPS World Defense PNT Contributing Editor

Tuesday, December 22, 2009

Sunday, December 20, 2009

UNCLOS: Sharing Benefits

Archive > November 2009, Volume 13, Number 09 > UNCLOS: Sharing Benefits
http://www.hydro-international.com/issues/articles/id1129-UNCLOS_Sha...

Hydro International Interviews Tullio Scovazzi Sharing benefits arising from the exploitation of mineral resources of the deep seabed between developed and developing countries is one of the main goals of the United Nations Convention on the Law of the Sea (UNCLOS) says professor Tullio Scovazzi, professor of International Law at the University of Milano-Bicocca, Milan (Italy)and one of Italy’s most renown experts on UNCLOS.
Giuseppe Angrisano, contributing editor, Hydro International Professor, you are one of the most renown Italian experts on UN Convention on the Law of the Sea (UNCLOS) issues. Can you tell the readers of Hydro international a little about your career and why you focused your studies towards this subject?
I prefer to avoid speaking about myself. As I teach international law, let me quote a proverb current in Italy. It's "chi sa, fa; chi non sa, insegna" and it means "he who knows, does; he who doesn't know, teaches". But if you insist, I can say that, as an academic, I have been attracted by the international law of the sea since the beginning of my studies. Then I had the possibility to participate in a number of international meetings as legal expert representing Italy for certain international institutions. With regard to international law of the sea, besides its many concrete aspects, it is characterised by a great intellectual attraction, arising from the fact that it ranges from the historical heritage of the past to the potential achievements of the future.

The UNCLOS is now operational but some important maritime states have not yet ratified it. In your opinion, what could be the reasons for such reluctance?
The UNCLOS has been ratified by 158 states so far; that is the large majority of countries in the world. The main state that is not a party is the USA. The USA is not satisfied with Part XI of the Convention, which relates to the greatly innovative concept of the common heritage of mankind, which is the sharing of the benefits arising from the exploitation of mineral resources of the deep seabed with developing countries. I regret that, for now, the richest country in the world takes such an attitude. The reason for other states that haven't ratified yet is mostly due to specific circumstances, such as maritime delimitation issues.

Article 76 of the UNCLOS states that after the Convention enters into force for a given State, it has 10 years to submit its claim for extending the limits of its continental shelf to the UN Commission on the Limits of the Continental Shelf (UN CLCS). Even if 10 years may seem a sufficient time frame, it may happen that a State
cannot collect the hydrographic data on time for a reasonable submission of the claim. Can you suggest a legal instrument to avoid this inconvenience? The 10-year deadline for the submission of claims to the UN CLCS is not a rigid one. In 2008, the Meeting of the States Party decided to impose the deadline of 13 May 2009 in a flexible way, as the lack of resources made it difficult for a number of countries to meet the deadline. It was decided that countries need not complete their full submission by the deadline, but can transmit preliminary information indicative of the outer limits of the continental shelf, along with a description of the status of preparation and the intended date when they will make a full submission. In fact, the
present problem is to find ways to enable the Commission to face its very heavy workload.

Once a State has submitted its claim to the UN CLCS and has met all the requirements of the Commission, in which way is its claim internationally recognised? Under the UNCLOS, the limits of the continental shelf established by a coastal State on the basis of the recommendations of the Commission are final and binding. In case of disagreement by the coastal State with the recommendations of the Commission, the coastal State shall, within a reasonable time, make a revised or new submission to the Commission. This means that no outer limit of the continental shelf can be established without the consent of the coastal State concerned.

In the Mediterranean there is no space for claiming any exclusive economic zone by any of the coastal States. Nevertheless, France and other countries established an ecological protection zone after the year 2000. How do you value that initiative? What are its advantages? The question is not fully correct. The fact that a State cannot claim a full-size 200-mile exclusive economic zone does not mean that it is
prevented from proclaiming such a zone. Exclusive economic zones have been established in other semi-enclosed seas, such as the Baltic and the Caribbean. Some Mediterranean States have already proclaimed an exclusive economic zone. The establishment of such a zone is the best way to face the shortcomings of the regime of the high seas, that is the absence of coastal State jurisdiction and the application of a regime based on flag State jurisdiction. This regime means in several cases the triumph of flags- of-convenience jurisdiction, with some unhappy consequences, such as a first-come-first-served approach leading to unsustainable fishing activities and a gross disregard for measures needed to protect the marine
environment. In conclusion, the establishment of exclusive economic zones by the coastal States and the consequent elimination of areas of high seas in the Mediterranean can only be seen as a very positive evolution towards a better governance of this sea.

In addition, in the Mediterranean, there are several bottom sea area delimitation treaties in force. What are the rights of the States on these areas?
The rights of the coastal State on the seabed adjacent to its territory (the continental shelf, in legal terms) have already been set forth in the 1958 Geneva Convention on the Continental Shelf and have been confirmed by the UNCLOS. They relate to the exploitation of mineral resources of the seabed and the subsoil thereof, as well as of the sedentary fishing resources. In the Mediterranean, some treaties of delimitation of the continental shelf have already been concluded by the two adjacent or opposite States concerned. In this case, the question is whether the limit in the superjacent waters should remain the same. Where no treaty exists, the
States concerned should start negotiations to delimit their respective marine spaces (fishing zones, ecological zones or, better still, exclusive economic zones).

How do you value the role of the National Hydrographic Offices and International Hydrographic Organization for the implementation of UNCLOS articles?
There are several provisions in the UNCLOS that have a technical character and make use of concepts with a scientific nature (such as high tide, low-water mark, nautical chart, straight baselines, routes of navigation having certain navigational and hydrographical characteristics, continental shelf, etc.). The role of national and international oceanographic institutions should be recognised and strengthened to ensure the full implementation of the UNCLOS, especially by developing countries.
Piracy has existed for many centuries already, but it has grown dramatically
in recent years - especially off the coast of Somalia. Is the UNCLOS regime adequate to meet the challenges posed by piracy within and beyond the territorial sea of Somalia? The recent events off the Somali coast and the resolutions adopted by the
UN Security Council to face piracy in this area show that the definition of piracy provided by the UNCLOS is too restrictive. In legal terms, acts of piracy can take place only beyond the 12-mile limit of the territorial sea. If this is the case, every State can seize the pirate ship, arrest the pirates and impose sanctions on them. However, if acts of depredation and violence are committed within the territorial sea of a coastal State, only this State is entitled to exercise its jurisdiction. This is the reason why many pirates are active within the territorial sea of a State incapable to exercise its jurisdiction, such as Somalia, or, if they act beyond, they try to return as soon as possible within the territorial sea of such State. The UNCLOS regime should be improved to meet the need to prevent and sanction piracy also within territorial seas, in case of persistent lack of law enforcement by the coastal States' authorities.

You have participated in works related to the UNESCO Convention on the Protection of the Underwater Cultural Heritage that was adopted by UNESCO at its General Conference held from 15 October to 3 November 2001. What is the status of ratification of this Convention? How does this Convention consider the wrecks from the Second World War: they are not older than 100 years (the antiquity prescribed by the Convention) but represent a value for the Nations that fought that war? In which way can the remains of what are sometimes important ships, such as the battleships Bismarck(Germany) and Roma (Italy), be protected?
The UNESCO Convention on the Protection of the Underwater Cultural Heritage entered into force on 2 January 2009 and is now binding in 26 States. It is a good convention, despite the complex character of some of its provisions. It even becomes extremely good if compared with the extremely bad regime provided for in Article 303, paragraph 3, of the UNCLOS. The latter can be intended as an incentive for the looting of the underwater cultural heritage, especially in the light of the application made by American courts of the so-called admiralty law. The fact that the UNESCO Convention applies only to heritage that has been underwater for at least 100 years does not prevent the adoption of national legislation providing for a shorter period. In the case of warships, their protection as war cemeteries is also
possible under national legislation.

Finally, the UNCLOS is a matter of great interest, especially now when issues of marine environment preservation and exploitation, marine transport (with 95% of merchandise being transported by sea) and naval operations have increased dramatically. Do you sea a future for young lawyers in finding a job in this particular field? Do you have a message for them?
There is a certain interest among students and young lawyers for law of the sea. Due to the progressive growth of maritime transportation of goods and commodities, private maritime law remains a promising field for lawyers, as it has been in the past. Today, questions of compensation for damage arising from pollution of the sea may determine litigation at both the domestic and international level. It is much less likely for a lawyer to be involved in litigation relating to public international law of the sea, even if cases of maritime delimitations are more frequent today than in the past. In addition, there are possibilities for finding an occupation within international organisations that are also responsible for maritime activities, such as the UN, International Maritime Organization, Food and Agriculture Organization (FAO) or the European Community.

Biography of the author
Tullio Scovazzi is a professor of International Law at the University of Milano- Bicocca, Milan (Italy). He is responsible for several research projects relating to the international law of the sea, environmental law and the regime of Antarctica. Scovazzi has represented the Government of Italy in a number of international negotiations, amongst others within the framework of the Mediterranean Action Plan, the International Seabed Authority, the UNCLOS, the Draft Convention on the Protection of the Underwater Cultural Heritage (1998–2000), and the UN Open-ended Informal Consultative Process on Oceans and the Law of the Sea (2000). He has consulted for the FAO and UN Environment Programme. He is the author of several books and articles on various topics, mostly in the fields of the international law of the sea, international environmental law and the regime of Antarctica.